Question

Mary _______ her mother with the housework, but she didn’t. A．must have helped ...

Mary _______ her mother with the housework, but she didn’t. A．must have helped B．ought to have helped C．must help D．should help

Answer 1

B

试题分析：考查情态动词用法。根据but后面的didn’t,说明本句是对过去情况的虚拟，故使用“情态动词+have done”的形式。Must have done一定做了某事；ought to have done本应该做某事，实际上却未做；CD两项是对现在情况的推测。句意：Mary本应该帮助妈妈做家务的，但是她却没有。故B正确。 点评：本题是高考必考考点，一定要牢记句型意思。must have done过去肯定做了某事。should have done 本应该做而实际未做。can’t have done 过去不可能做了某事；shouldn’t have done 本不应该做而实际做了。 need have done 本有必要做某事；needn’t have done 本没有必要做某事；注意没有 mustn’t have done的形式。