读短文，用所给动词的适当形式填空。

     When Miss Minnix was thirteen, she 1_____ (see) pictures of poor kids from Africa. When she saw the

pictures, she thought that one day she 2_____ (go) to Africa to help these kids. She waited for a very long

time before she 3_____ (grow) up. And then she was able 4_____ (go) there for the first time in the summer

of 2006. During her first visit to Africa, she and some other people 5_____ (start) a program for poor kids.

The program helped them go to school.

凡是在招标中因招标人泄露标底而签订的施工承包合同属于（）。

A．合同有效

B．无效合同

C．可撤销合同

D．合同效力待定