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: How does a chestnut tree form its heartwood?, Context: The term heartwood derives solely from its position and not from any vital importance to the tree. This is evidenced by the fact that a tree can thrive with its heart completely decayed. Some species begin to form heartwood very early in life, so having only a thin layer of live sapwood, while in others the change comes slowly. Thin sapwood is characteristic of such species as chestnut, black locust, mulberry, osage-orange, and sassafras, while in maple, ash, hickory, hackberry, beech, and pine, thick sapwood is the rule. Others never form heartwood.

SOLUTION: the change comes slowly

PROBLEM: The city state form of government eventually expanded to an?, Context: The period known as classical antiquity began with the rise of the city-states of Ancient Greece. Greek influence reached its zenith under the expansive empire of Alexander the Great, spreading throughout Asia.

SOLUTION: empire

PROBLEM: Which of Nanjing's sports centers bears its name?, Context: There are two major sports centers in Nanjing, Wutaishan Sports Center and Nanjing Olympic Sports Center. Both of these two are comprehensive sports centers, including stadium, gymnasium, natatorium, tennis court, etc. Wutaishan Sports Center was established in 1952 and it was one of the oldest and most advanced stadiums in early time of People's Republic of China.

SOLUTION:
Nanjing Olympic