题目

Legend has it that an apple which fell from its branches was the inspiration for Sir Isaac Newton’s discovery of gravity(引力). But now history’s famous fruit tree is paying the price of fame.                            The thousands of visitors drawn to Sir Isaac’s childhood home each year could be damaging the tree. A willow barrier(围栏)has been put around the tree. It means visitors to the 17th century Woolsthorpe Manor, near Grantham, Lincolnshire, will no longer be able to sit under its branches as Newton was said to have been doing in 1665 whe—             do you watch TV in the evening? — For about one hour. [     ]A. How long B. How often C. When D. What time