解析：unable 不能。

　　答案：unable

　　4．They were ________ sea when they met with a hurricane.

　　解析：at sea 在航海。

　　答案：at

　　5．I saw an old man ________ (rest) in the shade.

　　解析：see sb. doing sth. 看见某人在做某事。

　　答案：resting

　　6．The car was travelling ________ the opposite direction.

　　解析：in the opposite direction 朝相反方向。

　　答案：in

　　7．He escaped ________ (kill) by the cruel king.

　　解析：escape 后跟动名词作宾语，该处具有被动含义，故用 being done。

　　答案：being killed

　　8．The drowning boy was picked ________ by a passing boat.

　　解析：pick up 拾起，救起。

　　答案：up

　　9．He tried to make me ________ (understand) the theory.

　　解析：make sb. do sth. 让某人做某事。

答案：understand