By the time a child is five he hundreds of hours of television.A. will watchB. will have

问题补充：

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

答案：

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。