答案：In

　　3．Because ________ the traffic jam, we got stuck.

　　解析：because of 由于。

　　答案：of

　　4．You must decide ________ your plan.

　　解析：decide on 决定。

　　答案：on

　　5．His theory is too ________ (complicate)．

　　解析：形容词作表语。complicated 复杂的。

　　答案：complicated

　　6．There is a path ________ run parallel to the river.

　　解析：先行词为 path，定语从句中缺主语，故用 which/that。

　　答案：which/that

　　7．The aim of the project is ________ (examine) the transport situation.

　　解析：动词不定式作表语。

　　答案：to examine

　　8．We agreed ________ a solution ________ this problem.

　　解析：agree on 商定；solution 后跟 to。

　　答案：on; to

　　9．The shop is closing ________， so everything is at a discount.

　　解析：close down 关闭。

　　答案：down

　　10．He practised ________ (play) the violin every evening.

　　解析：practise 后跟动名词。

答案：playing