Crusaders, Mamelukes, and Turks: The Crusaders established a feudal Christian state with Godfrey at its head. They built many impressive churches during the term of the first Latin Kingdom of Jerusalem, but in 1187 they were driven out by Muslim forces under the great warrior Saladin. During the Sixth Crusade (1228 1229), the Holy Roman Emperor Frederick II managed to secure Jerusalem for the Christians by negotiation. The Christians, however, could not hold the city. After they lost Jerusalem, a Mongol invasion swept through, and in 1244 the Mameluke dynasty of Egypt took control, ruling Jerusalem for the next 250 years. The city struggled to rebuild from Crusader wars and invasions. Much of the best Islamic architecture in the city was constructed in the Mameluke era, but the past thousand years had taken their toll: Jerusalem was unable to regain the prosperity it had enjoyed in earlier times. In the early 16th century, the Ottoman Turkish Empire was advancing through the Middle East. Jerusalem fell to the Ottomans in 1517, remaining under their control for 400 years. Suleiman the Magnificent rebuilt the walls and gates in the form they retain to this day. Fountains, inns, religious schools, and barracks were constructed. But when Suleiman died, his empire, including Jerusalem, began a long period of decline. The Holy City remained a backwater until the 19th century, when renewed interest among Christian pilgrims made it the destination of thousands of travelers each year.

Question: "Who built many impressive churches during the term of the first Latin Kingdom of Jerusalem?"

OPTIONS:
- no
- yes

Answer: "Christians"

Response: no

You may wonder if there are other examples of static discharge. The answer is yes. Lightning is a form of static discharge. It is much more dramatic than what happens between you and the door knocker, but it is the same principle. You can see how it occurs in the following diagram and animation. You have no doubt seen lightning in a rainstorm. What does lighting have to do with static electricity? As it turns out, everything! During a rainstorm, clouds develop regions of different charges. This happens due to the movement of air molecules, water drops, and ice particles. The negative charges are concentrated at the base of the clouds. The positive charges are concentrated at the top. The negative charges repel electrons on the ground below. The ground then becomes positively charged. Over time the differences increase. Eventually the electrons are discharged. This is what we see as lightning. You can watch an awesome slow-motion lightning strike below.

Question: "How is the top of a cloud different from the base of the cloud during a rainstorm?"

OPTIONS:
- no
- yes

Answer: "Top and bottom clouds have opposite charges"

Response: yes

The inhabited history of the Las Vegas Valley stretches to 23,000 b.c. , when much of the area was covered by a prehistoric lake. During this period, the indigenous people lived in caves, hunting the mammals that gathered at the shoreline. The landscape of the valley changed dramatically over the next 200 centuries. The glaciers feeding the lake melted away and the lake evaporated. Fossils tell an obscure story of man's slow and sporadic development. Around 3000 b.c. , native Archaic Indians began to develop a lasting hunting and gathering culture. By this time, the valley was in much the same geographic state as it exists in today, with one exceptionthe presence of artesian springs that bubbled to the surface in several areas. These springs fed a network of streams draining through the Las Vegas Wash to the Colorado River. The areas surrounding the springs were desert oases: sprawling collections of grasses, trees, and wildlife. Many springs lay in areas that would eventually become the center of the modern Las Vegas metropolis. For about 4000 years, the Archaics thrived in a culture that included many signs of early civilization. Signs of even more advancement appeared halfway through the first millennium a.d. , when the Anasazi Indians inhabited the valley. Far more progressive than the Archaics, the Anasazi utilized such formal agricultural techniques as irrigation to assist their harvest. This permitted the Anasazi to achieve a benchmark of advanced societythe ability to live in permanent shelters year-round without need to follow wildlife. Mysteriously, the Anasazi vanished from the valley around a.d.

Question: "When did the native Archaic Indians develop a hunting and gathering culture?"

OPTIONS:
- no
- yes

Answer: "First millennium a.d"

Response: no

Imagine you are standing in a farm field in central Illinois. The land is so flat you can see for miles and miles. On a clear day, you might see a grain silo 20 miles away. You might think to yourself, it sure is flat around here. If you drive one hundred miles to the south, the landscape changes. In southern Illinois, there are rolling hills. Why do you think this is? What could have caused these features? There are no big rivers that may have eroded and deposited this material. The ground is capable of supporting grass and trees, so wind erosion would not explain it. To answer the question, you need to go back 12,000 years. Around 12,000 years ago, a giant ice sheet covered much of the Midwest United States. Springfield, Illinois, was covered by over a mile of ice. Its hard to imagine a mile thick sheet of ice. The massive ice sheet, called a glacier, caused the features on the land you see today. Where did glaciers go? Where can you see them today? Glaciers are masses of flowing ice.

Question: "Water and wind erosion called the geographical features in Illinois. True or False?"

OPTIONS:
- no
- yes

Answer: "False"

Response:
yes