He transplanted the young tree to the park it was the best time for it .A. whereB. whenC.

问题补充：

He transplanted the young tree to the park it was the best time for it .

A. where

B. when

C. what

D. that

答案：

A. where

(答案→)B. when

C. what

D. that

解析：考查状语从句。本题考查when引导的时间状语从句，表示“在……时候”，根据句意选择B。