1 . About three years ago, something terrible ______（happen）to me. (所给词的适当形式填空)

2 . Previously, we had fixed classrooms where students all ________ (sit) in rows. (所给词的适当形式填空)

3 . They ________________ a lot of money to charity last month and helped people in need. (contribute) （用单词适当形式填空）