单选题
Nobody saw the CEO at the seminar; he ______ at it
A、
couldn't have spoken
B、
couldn't speak
C、
mustn't have spoken
D、
shouldn't have spoken
【正确答案】
A
【答案解析】
couldn't do sth，不可能做某事(很有把握的猜测)，由于句中表示的是对过去情况的猜测，所以用couldn't have done结构，选A。
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