阅读下面短文，掌握大意，然后从各题所给的四个选项（A、B、C和D）中，选出最佳答案。
In a class I taught adults． I gave the class an assignment—going to visit someone they loved within the next week and saying，“I love you”．It had to be someone they had 1 said those words to before or at least they hadn’t 2those words with for a long time． It didn’t sound like a very 3 assignment until I realized that most of the students were over 35 and were 4in the decades when they were taught not to express emotions 5．So this was a very threatening assignment for some．
At the beginning of our 6class，I asked if someone wanted to share what 7when he/she told someone he/she loved him/her． I 8 expected one of the women to volunteer，as was usually the 9，but this time one of the men raised his hand and said，“Dennis，I was quite angry with you last week 10you gave us this assignment． I didn’t feel that I had anyone to say those 11to，and besides，why did you tell us to do something 12？But as I began driving home my conscience started 13 me． It was telling me that I knew exactly who I 14to say “I love you” to． Five years ago，my father and I had a serious disagreement． Since then，we 15 seeing each other unless we absolutely had to meet at Christmas or other family 16．But even then，we hardly spoke to each other． Last Tuesday I got home and 17 myself to tell my father I loved him． He was shocked and then burst out 18．He said he always loved 19．”
Hearing his talking，all of the class were 20 deeply．
的中点,BE交DC于点F,求证:AF2=AC·AD. 