问题
单项选择题
You ______ the experiment twice, not once.
A．should have carried out
B．shouldn't have carried out
C．haven't carried out
D．couldn't have carried out
答案
参考答案：A
解析：“should+不定式完成式”表示“本应该做而实际没有做”的虚拟语气含义。
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