It is really a challenge for me to finish it. In order not to be disturbed I spent three

问题补充：

It is really a challenge for me to finish it. In order not to be disturbed, I spent three days in my study surfing the internet to do the research.

A. locking

B. locked

C. to lock

D. lock

答案：

A. locking

(答案→)B. locked

C. to lock

D. lock

解析：考查非谓语动词。本题考查短语spend … (in) doing sth.花费……做某事，根据句意选B。