一、

1．and

2．but

3．or

4．and

5．or

6．nor

7．When

8．if

9．because

10．but

11．if

12．since

13．or

14．or

二、

1．what

2．when

3．whether

4．why

5．which

6．how

7．that

8．who

9．how many

10．how long

三、

1．studies→study

2．are→is

3．are→am

4．love→loves

四、

简单句：

These questions were too difficult for us to answer．

复合句：

These questions were so difficult that we couldn't answer them．