TASK DEFINITION: Based on the information present in the given passage, you need to write a correct answer to the given question. A correct answer is one that correctly and completely answers the question. Do not write answers that address the question partially or incorrectly. The correct answer must be contained in the given paragraph.
PROBLEM: Paragraph- Sent 1:  Bin Laden reportedly discussed the planes operation with KSM and Atef in a series of meetings in the spring of 1999 at the al Matar complex near Kandahar.
Sent 2: KSM's original concept of using one of the hijacked planes to make a media statement was scrapped, but  Bin Laden considered the basic idea feasible.
Sent 3:  Bin Laden, Atef, and KSM developed an initial list of targets.
Sent 4: These included the White House, the U.S. Capitol, the Pentagon, and the World Trade Center.
Sent 5: According to KSM,  Bin Laden wanted to destroy the White House and the Pentagon, KSM wanted to strike the World Trade Center, and all of them wanted to hit the Capitol.
Sent 6: No one else was involved in the initial selection of targets.
Sent 7:  Bin Laden also soon selected four individuals to serve as suicide operatives: Khalid al Mihdhar, Nawaf al Hazmi, Khallad, and Abu Bara al Yemeni.
Sent 8: During the al Matar meetings,  Bin Laden told KSM that Mihdhar and Hazmi were so eager to participate in an operation against the United States that they had already obtained U.S. visas.
Sent 9: KSM states that they had done so on their own after the suicide of their friend Azzam (Nashiri's cousin) in carrying out the Nairobi bombing.
Sent 10: KSM had not met them.
Sent 11: His only guidance from  Bin Laden was that the two should eventually go to the United States for pilot training.
Sent 12: Hazmi and Mihdhar were Saudi nationals, born in Mecca.
Sent 13: Like the others in this initial group of selectees, they were already experienced mujahideen.
Sent 14: They had traveled together to fight in Bosnia in a group that journeyed to the Balkans in 1995.
Sent 15: By the time Hazmi and Mihdhar were assigned to the planes operation in early 1999, they had visited Afghanistan on several occasions.
Sent 16: Khallad was another veteran mujahid, like much of his family.
Sent 17: His father had been expelled from Yemen because of his extremist views.
Sent 18: Khallad had grown up in Saudi Arabia, where his father knew  Bin Laden, Abdullah Azzam, and Omar Abdel Rahman (the "Blind Sheikh"). 
Question: Who decided to obtain U.S. visas after their friend committed suicide carrying out the Nairobi bombing?.

SOLUTION: Khalid al Mihdhar and Nawaf al Hazmi.

PROBLEM: Paragraph- Sent 1: Hundreds of thousands of years before China was to become the world's longest-running civilization, the prologue was enacted by means of the flicker of a carefully tended fire.
Sent 2: Peking Man, a forebear of Homo sapiens, achieved a mastery of fire.
Sent 3: We might call it the first Chinese invention.
Sent 4: Not that he devised flint and steel, matches, or any other way of creating fire.
Sent 5: Peking Man simply learned how to capture flame, perhaps from a forest fire, and keep it alight.
Sent 6: He thus enjoyed two revolutionary luxuries: light and heat.
Sent 7: Technologically and sociologically, it was a phenomenal breakthrough: with fire, communities could live year 'round in one cave, in which cooking and even smelting could be pursued.
Sent 8: And so, by 600,000 b.c., about 50 km (31 miles) southwest of present-day Beijing, the ancestors of mankind were ready to settle down.
Sent 9: Several hundred thousand years later, when Marco Polo reached the capital of China, he was astonished by a further development in fire technology.
Sent 10: The Chinese, he announced, used black stones dug out of mountains as fuel.
Sent 11: Europeans did not yet have a word for "coal," nor had they discovered a use for it.
Sent 12: The First Dynasty The confluence of mythology and history in China took place around 4,000 years ago during what is referred to as the Xia (Hsia) Dynasty.
Sent 13: This was still the Stone Age, but the people are thought to have made silk from thread produced by the worms they cultivated on the leaves of their mulberry trees.
Sent 14: And written language (which evolved as early as 4,500 to 5,000 years ago) was already in use, originally by oracles and then by official scribes — China's first scholars.
Sent 15: During the second of the quasi-legendary dynasties, the Shang (from about the 16th to 11th centuries b.c.), the Chinese developed an interest in art.
Sent 16: Careful geometric designs as well as dragon and bird motifs adorned bowls and implements.
Sent 17: And with the arrival of the Bronze Age, the Chinese created bronze vessels of such beauty and originality that, until modern times, archaeologists refused to believe they were cast 3,000 years ago.
Sent 18: The Shang Dynasty gave rise to the concept of one Chinese nation under one government. 
Question: This famous explorer , after reaching China's capital city reported that the Chinese used what color rocks to make fire?.

SOLUTION: Marco Polo was amazed they used black rocks for fuel.

PROBLEM: Paragraph- Sent 1: From Babylon, Alexander went to Susa, one of the Achaemenid capitals, and captured its legendary treasury.
Sent 2: He sent the bulk of his army to the Persian ceremonial capital of Persepolis via the Royal Road.
Sent 3: Alexander himself took selected troops on the direct route to the city.
Sent 4: He had to storm the pass of the Persian Gates (in the modern Zagros Mountains) which had been blocked by a Persian army under Ariobarzanes and then hurried to Persepolis before its garrison could loot the treasury.
Sent 5: On entering Persepolis, Alexander allowed his troops to loot the city for several days.
Sent 6: Alexander stayed in Persepolis for five months.
Sent 7: During his stay a fire broke out in the eastern palace of Xerxes and spread to the rest of the city.
Sent 8: Possible causes include a drunken accident or deliberate revenge for the burning of the Acropolis of Athens during the Second Persian War. 
Question: What incident happened that the possible causes may have been from a drunken accident or revenge?.

SOLUTION:
Drunken accident or deliberate revenge for the burning of the Acropolis.

