I was surprised that no one ____

I was surprised that no one ______ them of the danger.
A、warns
B、warned
C、has warned
D、had warned
【正确答案】：D
【题目解析】：宾语从句的动作发生在主句的动作之前，主句用了一般过去时，从句应该用过去完成时。答案为D。