By the time a child is five, he hundreds of hours of television.
A. will watch
B. will have watched
C. had watched
D. is watching
网友回答
A. will watch
(答案→)B. will have watched
C. had watched
D. is watching
解析：在时间状语从句中By the time+ 一般现在时态，表示的是将来，主句应用将来完成时态，句意：到一个孩子五岁的时候，他将会已经看了几百个小时的电视了。所以选B。