Problem: Extract the answer to the question from the following context. Question: The Royal Air Force is known by what abbreviation? Context: On 15 September 1940, known as the Battle of Britain Day, an RAF pilot, Ray Holmes of No. 504 Squadron RAF rammed a German bomber he believed was going to bomb the Palace. Holmes had run out of ammunition and made the quick decision to ram it. Holmes bailed out. Both aircraft crashed. In fact the Dornier Do 17 bomber was empty. It had already been damaged, two of its crew had been killed and the remainder bailed out. Its pilot, Feldwebel Robert Zehbe, landed, only to die later of wounds suffered during the attack. During the Dornier's descent, it somehow unloaded its bombs, one of which hit the Palace. It then crashed into the forecourt of London Victoria station. The bomber's engine was later exhibited at the Imperial War Museum in London. The British pilot became a King's Messenger after the war, and died at the age of 90 in 2005.

A: RAF

Problem: Extract the answer to the question from the following context. Question: what is the last word in the paragraph? Context: True aspirated voiced consonants, as opposed to murmured (breathy-voice) consonants such as the [b], [d], [] that are common in the languages of India, are extremely rare. They have been documented in Kelabit Taa, and the Kx'a languages. Reported aspirated voiced stops, affricates and clicks are [bp, dt, dts, dt, k, q, , , , , ].

A: are

Problem: Extract the answer to the question from the following context. Question: why do cracks form in the glacier Context: The top 50 m (160 ft) of a glacier are rigid because they are under low pressure. This upper section is known as the fracture zone and moves mostly as a single unit over the plastically flowing lower section. When a glacier moves through irregular terrain, cracks called crevasses develop in the fracture zone. Crevasses form due to differences in glacier velocity. If two rigid sections of a glacier move at different speeds and directions, shear forces cause them to break apart, opening a crevasse. Crevasses are seldom more than 46 m (150 ft) deep but in some cases can be 300 m (1,000 ft) or even deeper. Beneath this point, the plasticity of the ice is too great for cracks to form. Intersecting crevasses can create isolated peaks in the ice, called seracs.

A: differences in glacier velocity

Problem: Extract the answer to the question from the following context. Question: When did the distinct Greek political identity come back? Context: A distinct Greek political identity re-emerged in the 11th century in educated circles and became more forceful after the fall of Constantinople to the Crusaders of the Fourth Crusade in 1204, so that when the empire was revived in 1261, it became in many ways a Greek national state. That new notion of nationhood engendered a deep interest in the classical past culminating in the ideas of the Neoplatonist philosopher Gemistus Pletho, who abandoned Christianity. However, it was the combination of Orthodox Christianity with a specifically Greek identity that shaped the Greeks' notion of themselves in the empire's twilight years. The interest in the Classical Greek heritage was complemented by a renewed emphasis on Greek Orthodox identity, which was reinforced in the late Medieval and Ottoman Greeks' links with their fellow Orthodox Christians in the Russian Empire. These were further strengthened following the fall of the Empire of Trebizond in 1461, after which and until the second Russo-Turkish War of 1828-29 hundreds of thousands of Pontic Greeks fled or migrated from the Pontic Alps and Armenian Highlands to southern Russia and the Russian South Caucasus (see also Greeks in Russia, Greeks in Armenia, Greeks in Georgia, and Caucasian Greeks).

A:
1261