Mywalletisnowheretobefound.I_____itwhenIwasonthebus.
A、mustdropD
must have+done 用于推断过去某个时间肯定发生了的事情。
_____you understand this rule ，you‘ll have no difficulty in dealing with such problems.
_____youunderstandthisrule，you‘llhavenodifficultyindealingwithsuchproblems.
His article is better than_____in the class.
Williamhascuthissmoking_____tofivecigarettesaday.
“It was very cold testerday. ”
“_____.”
