I __that they must have set off A frighten B afrid C surprise D fear说明一下选项的意思,及他们的用法.

I __that they must have set off A frighten B afrid C surprise D fear说明一下选项的意思,及他们的用法.
I __that they must have set off A frighten B afrid C surprise D fear
说明一下选项的意思,及他们的用法.

I __that they must have set off A frighten B afrid C surprise D fear说明一下选项的意思,及他们的用法.
B用法同上,但A项+ed才是他说的,应该是吓别人的意思.

B
I'm afraid that...意思是“我恐怕……”
A是受到惊吓的意思，C是惊讶的意思，D是恐惧、害怕的意思。