I don't doubt ___the plan will be received.

问题描述:

I don't doubt ___the plan will be received.
A:that B:why C:whether D:when
为什么呢

A
doubt “怀疑”,用在否定句中表示“不怀疑”,说明后面的事情是确定的,所以不能用表疑问的连接词,所以选that.
相反,如果用在肯定句中,表示“怀疑”,说明后面的事情是不确定的,经常用whether(是否).