问题补充：
How I regretted the hours in the forest, I should have studied hard in the classroom.
A. wasting; when
B. to waste; when
C. wasting; where
D. to waste; where
答案：
(答案→)A. wasting; when
B. to waste; when
C. wasting; where
D. to waste; where
解析： regret doing 后悔做过……，从句上可知第二空是修饰hours 的定语从句。
