解析：该题答案为A.They each不等于each of…，each of这个词组作主语谓语用单数如each of the students hands in their homework，而they each作主语，谓语要随each前面的词来变化。
167.Not only ____ this machine but ____ it.A.can he run……can he repair B.can he run……he can repair
C.he can run……he can repair D.he can run……can he repair
解析：该题答案为B，在not only……but（also）句型中，只有but前面的部分倒装，but后面仍是正常语序。
168.____ that he went to sleep.A It was until midnight B That was until midnight
C It was not until midnight D That was not until midnight解析：该题答案为C.强调until结构时，要将否定词not移到until前。又如：He didn‘t leave until twelve改为It was not until twelve that he left.
169.There are a lot of students ____ in the class room.A talk B talking C talked D to talk
解析：该题正确答案为B.There be句型为倒装句，可换为A lot of students are talking in the class room.又如：There is a lot of noise heard out in the street.
170.While ____my homework，I heard a cry for help.A do B did C doing D having done
解析：该题答案为C.该空处省略了I‘m，相当于while I’m doing my home work.如：While playing guitar，he is singing.
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