Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Context: Weathering changes solid rock into sediments. Sediments are different sizes of rock particles. Boulders are sedi- ments; so is gravel. At the other end, silt and clay are also sediments. Weathering causes rocks at the Earths surface to change form. The new minerals that form are stable at the Earths surface. It takes a long time for a rock or mountain to weather. But a road can do so much more quickly. If you live in a part of the world that has cold winters, you may only have to wait one year to see a new road start to weather (Figure Mechanical weathering breaks rock into smaller pieces. These smaller pieces are just like the bigger rock; they are just smaller! The rock has broken without changing its composition. The smaller pieces have the same minerals in the same proportions. You could use the expression a chip off the old block to describe mechanical weathering! The main agents of mechanical weathering are water, ice, and wind. Rocks can break apart into smaller pieces in many ways. Ice wedging is common where water goes above and below its freezing point (Figure 9.2). This can happen in winter in the mid-latitudes or in colder climates in summer. Ice wedging is common in mountainous regions. This is how ice wedging works. When liquid water changes into solid ice, it increases in volume. You see this when you fill an ice cube tray with water and put it in the freezer. The ice cubes go to a higher level in the tray than the water. You also may have seen this if you put a can of soda into the freezer so that it cools down quickly. If you leave the can in the freezer too long, the liquid expands so much that it bends or pops the can. (For the record, water is very unusual. Most substances get smaller when they change from a liquid to a solid.) Abrasion is another type of mechanical weathering. With abrasion, one rock bumps against another rock. Gravity causes abrasion as a rock tumbles down a slope. Moving water causes abrasion it moves rocks so that they bump against one another (Figure 9.3). Strong winds cause abrasion by blasting sand against rock surfaces. Finally, the ice in glaciers cause abrasion. Pieces of rock embedded in ice at the bottom of a glacier scrape against the rock below. If you have ever collected beach glass or pebbles from a stream, you have witnessed the work of abrasion. Sometimes biological elements cause mechanical weathering. This can happen slowly. A plants roots grow into a crack in rock. As the roots grow larger, they wedge open the crack. Burrowing animals can also cause weathering. By digging for food or creating a hole to live in the animal may break apart rock. Today, human beings do a lot of mechanical weathering whenever we dig or blast into rock. This is common when we build homes, roads, and subways, or quarry stone for construction or other uses. Mechanical weathering increases the rate of chemical weathering. As rock breaks into smaller pieces, the surface area of the pieces increases. With more surfaces exposed, there are more places for chemical weathering to occur. Lets say you wanted to make some hot chocolate on a cold day. It would be hard to get a big chunk of chocolate to dissolve in your milk or hot water. Maybe you could make hot chocolate from some smaller pieces like chocolate chips, but it is much easier to add a powder to your milk. This is because the smaller the pieces are, the more surface area they have. Smaller pieces dissolve more easily. Chemical weathering is different than mechanical weathering. The minerals in the rock change. The rock changes composition and becomes a different type of rock. Most minerals form at high pressure or high temperatures deep within Earth. But at Earths surface, temperatures and pressures are much lower. Minerals that were stable deeper in the crust are not stable at the surface. Thats why chemical weathering happens. Minerals that formed at higher temperature and pressure change into minerals that are stable at the surface. Chemical weathering is important. It 
 Question: weathering process that occurs when rocks and rock particles scrape other rocks
abrasion

Context: The movie starts off with archive black-and-white footage of the Nazi's atrocities on the Jews across Europe. The focus shifts to West Belarus, where Nazi SS soldiers, under the command of Bernicki, the Belarussian Police Captain, are busy "sanitizing" a village, killing half the people and abducting the rest. Zus Bielski (Liev Schreiber) and his brother, Asael (Jamie Bell), watch helplessly from the forest. Once the Germans have left, they run to the village and are devastated to find their father dead. They go to their house and find their youngest brother, Aron (George MacKay), cowering under the floorboards in the closet. They take him with them to the forest.In the Lipiczanska Forest, Zus tells a weeping Asael to get a hold of himself. As they sleep, their eldest brother, Tuvia Bielski (Daniel Craig), walks up to them and wakes them up. He first admonishes Asael for not being alert, then embraces him and Aron emotionally. Zus and Tuvia have a rather curt reunion. As they walk into the forest, Zus tells Tuvia that his wife and child are hiding in a village. At night, they discuss their options. The police are after them, however they are safe in the woods. They talk about Bernicki. A friend, Koscik has a gun which they can borrow. Next morning, Aron stumbles across some other Jewish refugees in the forest. He brings them back to his brothers. One of them is a young child, mortally wounded. Unfortunately, they can't save her. As her parents grieve, Zus tells Tuvia that they can't support these people. Tuvia says he'll ask Koscik for food and his pistol.In the nearby village, Konstanty 'Koscik' Kozlowski, their friend and a secret Jew-sympathizer, lets Tuvia inside and gives him food, drink and his pistol, with only 4 bullets. Seeing a police car coming towards the house, Koscik hides Tuvia in the barn, along with some other Jews. It's Bernicki and his sons, who Koscik welcomes warmly. Bernicki talks about his Jew-hunting exploits. Bernicki talks about having killed the Bielskis' father and is now after the sons. He tells Koscik to keep his eyes open and leaves. After they're gone, Koscik gives Tuvia food and drink and asks him to take the Jews from his barn. Tuvia confirms that Bernicki and his sons were responsible for his parent's deaths. He then takes the other Jews and goes into the forest.As they walk into the forest, one of the Jews, an elderly man named Shamon Haretz, Tuvia's old school-teacher, talks to him about his experiences. Tuvia brushes him off. At the campsite, the food is being passed around, with each person taking a small morsel so the others can have some. Zus is upset that Tuvia brought more mouths to feed. Tuvia tells him that it was Bernicki who killed their parents. That night, he goes to Bernicki's house, where he is having dinner with his wife and two sons. Tuvia bursts inside and holds them at gunpoint. He asks them if he knows who he is and why he's there. Terrified, Bernicki says he did as ordered. Tuvia orders him to his knees. Bernicki's sons jump up to their father's aid, but Tuvia shoots them dead. He then shoots Bernicki dead. Bernicki's hysterical wife pleads with Tuvia to kill her as well. Leaving her alive and grief-stricken, he leaves.The next morning, Tuvia tells Zus he killed Bernicki and his sons. They decide to move deeper into the woods. Tuvia brings over more Jews, much to Zus' displeasure. One of them is Isaac Malbin (Mark Feuerstein). The refugees start building makeshift houses in the woods. After almost hitting Zus with a log, Isaac confesses that he's an intellectual, not a carpenter. A refugee introduces Tuvia to his "forest wife". Tuvia congratulates them, a bit unsurely. Just then, two men burst into the scene, one of them holding a rifle, while 
 Question: Where did the brothers flee?
into another part of the woods.

Context: Radioactivity is the ability of an atom to emit, or give off, charged particles and energy from the nucleus. The charged particles and energy are called by the general term radiation. Only unstable nuclei emit radiation. When they do, they gain or lose protons. Then the atoms become different elements. (Be careful not to confuse this radiation with electromagnetic radiation, which has to do with the light given off by atoms as they absorb and then emit energy.) Radioactivity was discovered in 1896 by a French physicist named Antoine Henri Becquerel. Becquerel was experimenting with uranium, which glows after being exposed to sunlight. Becquerel wanted to see if the glow was caused by rays of energy, like rays of light and X-rays. He placed a bit of uranium on a photographic plate. The plate was similar to film thats used today to take X-rays. You can see an example of an X-ray in Figure 11.1. As Becquerel predicted, the uranium left an image on the photographic plate. This meant that uranium gives off rays after being exposed to sunlight. Becquerel was a good scientist, so he wanted to repeat his experiment to confirm his results. He placed more uranium on another photographic plate. However, the day had turned cloudy, so he tucked the plate and uranium in a drawer to try again another day. He wasnt expecting the uranium to leave an image on the plate without being exposed to sunlight. To his surprise, there was an image on the plate in the drawer the next day. Becquerel had discovered that uranium gives off rays without getting energy from light. He had discovered radioactivity, for which he received a Nobel prize. To learn more about the importance of Becquerels research, go to this URL: [Link] Another scientist, who worked with Becquerel, actually came up with the term "radioactivity." The other scientist was the French chemist Marie Curie. She went on to discover the radioactive elements polonium and radium. She won two Nobel Prizes for her discoveries. You can learn more about Marie Curie at this URL: [Link] Isotopes are atoms of the same element that differ from each other because they have different numbers of neutrons. Many elements have one or more isotopes that are radioactive. Radioactive isotopes are called radioisotopes. An example of a radioisotope is carbon-14. All carbon atoms have 6 protons, and most have 6 neutrons. These carbon atoms are called carbon-12, where 12 is the mass number (6 protons + 6 neutrons). A tiny percentage of carbon atoms have 8 neutrons instead of the usual 6. These atoms are called carbon-14 (6 protons + 8 neutrons). The nuclei of carbon-14 are unstable because they have too many neutrons. To be stable, a small nucleus like carbon, with just 6 protons, must have a 1:1 ratio of protons to neutrons. In other words, it must have the same number of neutrons as protons. In a large nucleus, with many protons, the ratio must be 2:1 or even 3:1 protons to neutrons. In elements with more than 83 protons, all the isotopes are radioactive (see Figure 11.2). The force of repulsion among all those protons overcomes the strong force holding them together. This makes the nuclei unstable and radioactive. Elements with more than 92 protons have such unstable nuclei that these elements do not even exist in nature. They exist only if they are created in a lab. A low level of radiation occurs naturally in the environment. This is called background radiation. It comes from various sources. One source is rocks, which may contain small amounts of radioactive elements such as uranium. Another source is cosmic rays. These are charged particles that arrive on Earth from outer space. Background radiation is generally considered to be safe for living things. A source of radiation that may be more dangerous is radon. Radon is a radioactive gas that forms in rocks underground. It can seep into basements and get trapped inside buildings. Then it may build up and become harmful to people who breathe it. Other sources of radiation are described in the interactive animation at this URL: [Link] You may have seen a sign like 
 Question: charged particles and energy emitted by an unstable nucleus

radiation