Which do you enjoy your spare time surfing the Internet or building up your strength?A.

问题补充：

Which do you enjoy your spare time, surfing the Internet or building up your strength?

A. to spend

B. spend

C. spending

D. to spending

答案：

(答案→)A. to spend

B. spend

C. spending

D. to spending

解析：考查非谓语动词。此处使用不定式表示目的，enjoy的宾语是surfing the Internet or building up your strength，即为了度过你的空余时间，选A。