Earths magnetic field helps protect Earth and its organisms. It protects us from harmful particles given off by the sun. Most of the particles are attracted to the north and south magnetic poles. This is where Earths magnetic field is strongest. This is also where relatively few organisms live. Another benefit of Earths magnetic field is its use for navigation. People use compasses to detect Earths magnetic north pole. Knowing this helps them tell direction. Many animals have natural 'compasses' that work just as well. Birds like the garden warbler in Figure 1.36 use Earths magnetic field. They use it to guide their annual migrations. Recent research suggests that warblers and other migrating birds have structures in their eyes. These structures let them see Earths magnetic field as a visual pattern.

Question: "According to this passage, what protects the organisms of Earth from harmful particles given off by the sun?"

OPTIONS:
- no
- yes

Answer: "Sun's magnetic field"

Response: no

If you build a campfire, you start with a large stack of sticks and logs. As the fire burns, the stack slowly shrinks. By the end of the evening, all that is left is a small pile of ashes. What happened to the matter that you started with? Was it destroyed by the flames? It may seem that way. What do you think happened? The truth is that the same amount of matter still exists. The wood changed not only to ashes, but also to carbon dioxide, water vapor, and other gases. The gases floated off into the air, leaving behind just the ashes. Although matter was changed, it was not created or destroyed. Because the same amount of matter still exists, we can say that matter is conserved. You may wonder how it can be conserved if something is now missing? Assume you had measured the mass of the wood before you burned it. Assume you had also trapped the gases released by the burning wood and measured their mass and the mass of the ashes. What would you find? The ashes and gases combined have the same mass as the wood you started with. This example illustrates the law of conservation of mass.

Question: "What is left when the stack shrinks?"

Response: "Small pile of ashes"
OPTIONS:
- no
- yes

A: yes

Problem: Little is known of the earliest Stone Age inhabitants of Europe's southwestern extremity. The ancient Greeks called them the Cynetes (or Cunetes). Whatever their origins, their culture evolved under the pressure and influence of foreign forces. Among the many invading armies that settled here and contributed to nascent Portuguese culture were Phoenicians, who settled in the area around 1,000 b.c., followed by the Celts, Iberians, Greeks, and Carthaginians. But it was the Romans, who arrived late in the third century b.c., who most greatly influenced all of Iberia. They built towns, industries, roads, and bridges, developed agriculture, and bequeathed the Latin language, of which Portuguese is a direct descendant. The Romans named the southwestern province of the peninsula Lusitania, oddly enough for one of the Celtiberian tribes they defeated, and by the third century a.d. had introduced Christianity. By the beginning of the fourth century the Algarve had a bishop in place, based in Faro. But Rome had already fallen into decay, and soon hordes of northern tribesmen took over the empire. The Algarve fell to the Visigoths in the mid-fifth century. Under Moorish Rule In a.d. 711, the Moors brought powerful armies from North Africa and launched a devastating attack on the Iberian peninsula, conquering much of what would become Spain and Portugal. They imposed Islam and left an indelible influence on the countryside and the population of the Algarve. The Moorish legacy can still be seen in the form of wells and waterwheels, squat white houses, the dark complexions of the people, and in the very name given the regiontaken from Al-Gharb, which means "country of the west" (when the Moors conquered the territory, it was the most westerly in the known world). The Moors governed their Iberian kingdoms from across the border in Seville, but the Algarve had its own regional capital and huge, invulnerable fortress. The capital was Chelb (or Xelb), and it was bigger and better defended than Lisbon. Today the town, known as Silves, is a provincial outpost whose only besiegers are busloads of tourists who climb the narrow streets up to the old Moorish ramparts.

Question: "Who built towns, roads and industries of Europe's southwestern extremity?"

Answer: "Greeks"

OPTIONS:
- no
- yes
Answer: no

A flood occurs when a river overflows its banks. This might happen because of heavy rains. Floodplains In very flat regions, flood water may spread out on the surface of the land. It then slows down and drops its sediment. If a river floods often, a floodplain develops. A floodplain is an area where a thick layer of rich soil is left behind as the floodwater recedes. Thats why floodplains are usually good places for growing plants. They are very flat areas and they have very rich soils. The Nile River valley is a great example of a floodplain. Each year, the Nile River rises over its banks. This floodwater carries a lot of sediment. This sediment has been eroded off areas of land from upstream. This sediment is dropped as the water slows down after spreading across the land. What is left behind is a very rich soil. Thats why crops can be raised in the middle of a sandy desert. Natural Levees A flooding river often forms natural levees along its banks. A levee is a raised strip of sediments deposited close to the waters edge.

Question: "What two geographic formation can be created from flooding rivers?"

OPTIONS:
- no
- yes

Answer: "Waters edge"

Response:
no