问题补充：
John usually relaxes himself by after he finishes his homework.
A. going online
B. played soccer
C. listen to music
D. to watch TV
答案：
(答案→)A. going online
B. played soccer
C. listen to music
D. to watch TV
解析：句意：John做完作业后经常上网来放松自己。介词by，表示通过某种方式，后面接动词的ing形式，故选A。
