Bob had thought his computer was broken _______ his little brother pointed out that he had forgotten to turn it on.

A. if                               B. before      C. after       D. because

（2010·湖南醴陵二中高三上第二次月考）    23. Bob had thought his computer was broken _______ his little brother pointed out that he had forgotten to turn it on.

A. if              B. before C. after       D. because