21. take up; left off　 22. took up　 23. taken to　 24. for the time being　 25. lose sight of　 26. what　 27. what　 28. what　 29. what　 30. as they are

5.We walked the length of the street.我们从街这头走到那头。

(21)1. A team of nurses assisted the doctor in performing the operation. 一组护士协助医生施行手术。 2. He asked us to assist him in carrying through his plan.他请求我们帮他完成他的计划。

(22)1. The floor requires washing.这地板该洗了。注意doing。 2. All passengers are required to show their tickets.所有乘客都必须出示车票。 3.The director required that we (should) work all night.主任要求我们通宵工作。

可以用suggest, order, insist, demand 等，同时注意当这些词用作名词时的虚拟用法。

3. Size of pension depends on length of service with the company.养老金的多少取决於为公司服务年限的长短. 4. At length the bus arrived, forty minutes late. 公共汽车终於来了, 晚了四十分钟.

4.He studied chemistry and then switched to biology.他原来学化学，后来改学生物。

(20)1. The room is 15 feet in length and 10 feet in breadth.这房间长15英尺，宽10英尺。 2. This car will turn in its own length.这种汽车可以在自身长度范围内掉头.

3.You pressed the wrong switch.你按错了开关。

5. I'm very pressed for cash at the moment can I pay you next week?我现在手头很紧－－下周再付给你行吗？ 6. My boot is pressing against a blister on my toe.我的靴子挤压了我脚趾上的水泡。

(19)1. Our glasses have been switched this is mine. 咱们的玻璃杯对调了－－这个是我的。 2. Long lectures really switch me off.我觉得冗长的演讲很烦人。

4. The child pressed her nose against the window.

2. Can you have your report ready for the press by next week?你的报告能在下星期赶好付印吗？ 3. The power of the press is very great.

2. You'll make your back ache if you carry those heavy buckets.

(18)1. Press this button to start the engine.