TASK DEFINITION: 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.
PROBLEM: Context: A cell is the smallest structural and functional unit of an organism. Some organisms, like bacteria, consist of only one cell. Big organisms, like humans, consist of trillions of cells. Compare a human to a banana. On the outside, they look very different, but if you look close enough youll see that their cells are actually very similar. Most cells are so small that you cannot see them without the help of a microscope. It was not until 1665 that English scientist Robert Hooke invented a basic light microscope and observed cells for the first time, by looking at a piece of cork. You may use light microscopes in the classroom. You can use a light microscope to see cells ( Figure 1.1). But many structures in the cell are too small to see with a light microscope. So, what do you do if you want to see the tiny structures inside of cells? In the 1950s, scientists developed more powerful microscopes. A light microscope sends a beam of light through a specimen, or the object you are studying. A more powerful microscope, called an electron microscope, passes a beam of electrons through the specimen. Sending electrons through a cell allows us to see its smallest parts, even the parts inside the cell ( Figure 1.2). Without electron microscopes, we would not know what the inside of a cell looked like. The outline of onion cells are visible under a light microscope. In 1858, after using microscopes much better than Hookes first microscope, Rudolf Virchow developed the hypoth- esis that cells only come from other cells. For example, bacteria, which are single-celled organisms, divide in half (after they grow some) to make new bacteria. In the same way, your body makes new cells by dividing the cells you already have. In all cases, cells only come from cells that have existed before. This idea led to the development of one of the most important theories in biology, the cell theory. Cell theory states that: 1. All organisms are composed of cells. 2. Cells are alive and the basic living units of organization in all organisms. 3. All cells come from other cells. As with other scientific theories, many hundreds, if not thousands, of experiments support the cell theory. Since Virchow created the theory, no evidence has ever been identified to contradict it. Although cells share many of the same features and structures, they also can be very different ( Figure 1.3). Each cell in your body is designed for a specific task. In other words, the cells function is partly based on the cells structure. For example: Red blood cells are shaped with a pocket that traps oxygen and brings it to other body cells. Nerve cells are long and stringy in order to form a line of communication with other nerve cells, like a wire. Because of this shape, they can quickly send signals, such as the feeling of touching a hot stove, to your brain. Skin cells are flat and fit tightly together to protect your body. As you can see, cells are shaped in ways that help them do their jobs. Multicellular (many-celled) organisms have many types of specialized cells in their bodies. Red blood cells (left) are specialized to carry oxygen in the blood. Neurons (cen- ter ) are shaped to conduct electrical im- pulses to many other nerve cells. These epidermal cells (right) make up the skin of plants. Note how the cells fit tightly together. While cells are the basic units of an organism, groups of cells can perform a job together. These cells are called specialized because they have a special job. Specialized cells can be organized into tissues. For example, your liver cells are organized into liver tissue. Your liver tissue is further organized into an organ, your liver. Organs are formed from two or more specialized tissues working together to perform a job. All organs, from your heart to your liver, are made up of an organized group of tissues. These organs are part of a larger system, the organ systems. For example, your brain works 
 Question: when were cells observed for the first time?

SOLUTION: 1665

PROBLEM: Context: Stress is the force applied to an object. In geology, stress is the force per unit area that is placed on a rock. Four types of stresses act on materials. A deeply buried rock is pushed down by the weight of all the material above it. Since the rock cannot move, it cannot deform. This is called confining stress. Compression squeezes rocks together, causing rocks to fold or fracture (break) (Figure 1.1). Compression is the most common stress at convergent plate boundaries. Stress caused these rocks to fracture. Rocks that are pulled apart are under tension. Rocks under tension lengthen or break apart. Tension is the major type of stress at divergent plate boundaries. When forces are parallel but moving in opposite directions, the stress is called shear (Figure 1.2). Shear stress is the most common stress at transform plate boundaries. Shearing in rocks. The white quartz vein has been elongated by shear. When stress causes a material to change shape, it has undergone strain or deformation. Deformed rocks are common in geologically active areas. A rocks response to stress depends on the rock type, the surrounding temperature, the pressure conditions the rock is under, the length of time the rock is under stress, and the type of stress. Rocks have three possible responses to increasing stress (illustrated in Figure 1.3): elastic deformation: the rock returns to its original shape when the stress is removed. plastic deformation: the rock does not return to its original shape when the stress is removed. fracture: the rock breaks. Under what conditions do you think a rock is more likely to fracture? Is it more likely to break deep within Earths crust or at the surface? What if the stress applied is sharp rather than gradual? At the Earths surface, rocks usually break quite quickly, but deeper in the crust, where temperatures and pressures are higher, rocks are more likely to deform plastically. Sudden stress, such as a hit with a hammer, is more likely to make a rock break. Stress applied over time often leads to plastic deformation. Click image to the left or use the URL below. URL: 
 Question: rocks that are pulled apart are under

SOLUTION: tension

PROBLEM: Context: An earthquake is sudden ground movement caused by the sudden release of energy stored in rocks. Earthquakes happen when so much stress builds up in the rocks that the rocks rupture. The energy is transmitted by seismic waves. Earthquakes can be so small they go completely unnoticed, or so large that it can take years for a region to recover. The description of how earthquakes occur is called elastic rebound theory (Figure 1.1). Elastic rebound theory. Stresses build on both sides of a fault, causing the rocks to deform plastically (Time 2). When the stresses become too great, the rocks break and end up in a different location (Time 3). This releases the built up energy and creates an earthquake. Click image to the left or use the URL below. URL: In an earthquake, the initial point where the rocks rupture in the crust is called the focus. The epicenter is the point on the land surface that is directly above the focus (Figure 1.2). In the vertical cross section of crust, there are two features labeled - the focus and the epicenter, which is directly above the focus. Click image to the left or use the URL below. URL: 
 Question: the theory that stress builds up in rocks until they can no longer bend so they break, causing an earthquake is

SOLUTION:
elastic rebound theory