TASK DEFINITION: In this task, you are given a question and a context passage. You have to answer the question based on the given passage.
PROBLEM: From what era, once thought devoid of animal life, was evidence of grazer populations discovered?, Context: Some paleontologists suggest that animals appeared much earlier than the Cambrian explosion, possibly as early as 1 billion years ago. Trace fossils such as tracks and burrows found in the Tonian period indicate the presence of triploblastic worms, like metazoans, roughly as large (about 5 mm wide) and complex as earthworms. During the beginning of the Tonian period around 1 billion years ago, there was a decrease in Stromatolite diversity, which may indicate the appearance of grazing animals, since stromatolite diversity increased when grazing animals went extinct at the End Permian and End Ordovician extinction events, and decreased shortly after the grazer populations recovered. However the discovery that tracks very similar to these early trace fossils are produced today by the giant single-celled protist Gromia sphaerica casts doubt on their interpretation as evidence of early animal evolution.

SOLUTION: the Tonian period

PROBLEM: Whose submarines, between the Germans and Soviets, were the Bermuda bases first used to look out for?, Context: Construction began in 1941 of two airbases consisting of 5.8 km2 (2.2 sq mi) of land, largely reclaimed from the sea. For many years, Bermuda's bases were used by US Air Force transport and refuelling aircraft and by US Navy aircraft patrolling the Atlantic for enemy submarines, first German and, later, Soviet. The principal installation, Kindley Air Force Base on the eastern coast, was transferred to the US Navy in 1970 and redesignated Naval Air Station Bermuda. As a naval air station, the base continued to host both transient and deployed USN and USAF aircraft, as well as transitioning or deployed Royal Air Force and Canadian Forces aircraft.

SOLUTION: German

PROBLEM: When did the first world war occur?, Context: The war has been described as the first "world war", although this label was also given to various earlier conflicts like the Eighty Years' War, the Thirty Years' War, the War of the Spanish Succession and the War of the Austrian Succession, and to later conflicts like the Napoleonic Wars. The term "Second Hundred Years' War" has been used in order to describe the almost continuous level of world-wide conflict during the entire 18th century, reminiscent of the more famous and compact struggle of the 14th century.

SOLUTION:
18th century