So difficult _______it to work out the problem that I decided to ask Tom for some advice.

A．I did find

B．did I find

C．I’ve found

D．have I found

为班级作贡献就是[     ]

①做好班级分配给自己的事

②主动为班级做力所能及的事

③定要当选为班长，管理班级

A．①③

B．②③

C．①②

D．①②③