Question

While dancing happily at home,_______________ ．

A．the door bell rang	B．the door bell rings
C．we heard the door bell rings	D．we heard the door bell ring

Answer 1

D

由句子结构上看，前后的动作执行者应该一致，所以排除A和B。C想是个宾语从句，要注意时态一致，如果将rings改成rang才可以。