根据下面资料，回答21-35题
In the past, I always thought that being a teacher was an easy job. But I changed my（21）when I became a part-time teacher. About four years ago, Richard asked me（22）I could help teach his students how to make a website about themselves.
I（23）because computer is what I do well and I didn′ t think teaching computer would bethat（24）.
But when 1 taught Richard′ s class, some of the students（25）with their friends while I was explaining how to do something. At first I just got angry with them,（26）Richard taught me to think why they were doing this. He said that if he was（27）a lesson and the students were not lis-tening, then he was angry with（28）for not making the lesson clear or interesting for them. I told him that I didn′ t（29）his idea. He then asked me if l had ever（30）the same thing. That made me stop. Of course I had !
If any of my past teachers are（31）this, I want to say sorry if I sometimes played around in the class（32）you were teaching. I didn′ t think how that would make you feel. I promise I will do my best to be a good（33）in the future. Please help us when we don′t understand and most（34）, don′ t be quick to be angry when we fail.（35）of us are perfect but with your help we can be successful.
第（22）题选
A.where
B.why
C.whether
D.when