If Charles had spent half as much time attending his classes as he did complaining about them, he would have been a good student.
A had spent half as much time attending his classes as he did complaining
B had spent half as much time attending his classes as he did to complain
C were to spend half as much time attending his classes as he does complaining
D were to spend half as much time attending his classes as complaining
E should spend half as much time attending his classes as to complain
the answer is A
但是注動詞後面為什麼會加ing?