通读下面的短文，掌握其大意。然后，从每小题的四个选择项中选出可填入相应空白处的最佳选项。

     In the past, I always thought that being a teacher was an easy job. But I changed my  when I became a part-time teacher. About four years ago, Richard asked me  I could help teach his students how to make website about themselves.
     I  because computer is what I do well and I didn't think teaching computer would be that .
     But when I taught Richard's class, some of the students  with their friends while I was explaining how to do something. At first I just got angry with them,  Richard taught me to think why they were doing this. He said that if he was  a lesson and the students were not listening, then he was angry with  for not making the lesson clear or interesting for them. I told him that I didn't  his idea. He then asked me if I had ever  the same thing. That made me stop. Of course I had！
     If any of my past teachers are  this, I want to say sorry if I sometimes played around in the class  you were teaching. I didn't think how that would make you feel. I promise I will do my best to be a good  in the future. Please help us when we don't understand and most , don't be quick to be angry when we fail.  of us are perfect but with your help we can be successful.