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
网友回答
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。