– I ran 10 miles last weekend. Can you believe that?
– Wow, that easy!
A. mustn' t be
B. mustn't have been
C. can't have been
D. couldn’t be
网友回答
A. mustn' t be
B. mustn't have been
(答案→)C. can't have been
D. couldn’t be
解析：
试题分析:考查情态动词。must 表示推测不用于否定句，排除A、B选项，而根据last weekend可知这是对过去的推测，应该用情态动词+have done，所以C选项正确。句意：--我上周跑了十英里。你相信吗？--哇，那肯定不容易吧！