答案：
1-5 CDACA
1. 选C ①let off原谅，不处罚，放过With your record, you can hardly expect to let off lightly.
②let down使失望，食言③let alone别管，别烦Let her alone! She didn’t pick a quarrel with you.④let out让……离开Open the door and let the cat out.
2. 选D ①delete消去，删除Delete his name from the list of applicants.②compel强迫，迫使(运用权利/力量对方采取行动)He was compelled by illness to give up his studies.③constrain 限制，约束(强调内心情感)，后接不定式His activities must be constrained.④repel排斥，抵制，防，抗We should not repel but protect young people’s enthusiasm.
3.选A 依语意以句子结构，此处需要一个代词，表泛指，则选one;而the one表特指Please get the chair for me, the one in the corner.
4.选C ①part 不及物动词 “分别，离别”Scarcely an hour has passed since we parted.②divide分，划分Is the land to be divided up or sold as a whole?③separate使……分离④abandon抛弃，放弃The order was given to abandon ship.
5.①take effect(药物)见效，(法律等)生效The new system of taxation will take effect next May.②take part参加③take place发生，举行④take turns轮流，依次They are unwilling to take turns at the same computer.