He laughed so much that he set her ________ too.

A.laughed

B.laughing

C.laugh

D.to laugh

答案及解析： B

解析：

set sb doing sth．使某人做起某事来或处于做某事的状态中；

set sb．to do sth．要某人做某事。句意：他笑得如此厉害以至于使她也笑了起来。