1、the key to solving the problem 中的 to是介词吗？固定用法？

2、the telephone···before it answered.
answer为什么不用被动语态？

3、I tried to phone her,but even as I____she was leaving the building.
为什么选had phoned？？？

4、-He ought to have been warned of danger.
-______,but he wouldn't listen to me.
答案是so he was,为什么不是Yes,he ought to？？

5、It's nearly 7,Jack _____be here at any moment.
我碰倒过两次这道题，但答案一个是should，一个是 can，到底是哪个？？

6、____more interesting.
为什么选quite a lot，而不选 quite？？？

7、This is twice as __large island as that.
填不填a？？？为什么？

8、The cheif reason for the population growth isn't so much a rise in birth rates______a fall in death as a result of improments in medical care.
为什么选as ，而不选 but。not...but...不是···而是···在句中讲的通些呀~~~~~

1、是。此外还有get down to，answer to，a guide to，introduction to等的to都作介词
2、省略句，before it（is）answered
3、表示过去的过去，用过去完成词
4、前句虚拟（他本应该的……），后句表实际情况，不虚拟。
5、should，表示应该，根据语境，快7点了，JACK应该在任何时候都（等候）在这里（而他现在没来）
6、quite不修饰比较级，需要用 a lot ,even much still 等来形容，题中 quite 用来修饰 a lot
类似的：Thank you very much。不能说thank you very 。可以说thank you much 。 此处 very修饰much
7、填a，This is an island twice as large as that one。
8、as a fall in death表示和死亡率一样