— Where is Lucy, Jane? 

— I am not sure. _____. [ ]

A. She must have gone home

B. She can't have gone home

C. She should have gone home

D. She might have gone home

收受定金的一方不履行约定的债务的，应当（）返还定金。

A.单倍

B.双倍

C.三倍

D.四倍