In order not to be disturbed ,I spent three hours _____ in m

常见考点：spend some time (in) doing something
而此处,考虑到逻辑主语I和lock的关系是被动,所以用locked,即过去分词来作补语,符合英语五大句型结构中的主谓宾补的结构.
补语由形容词,名词,不定式,现在分词,过去分词充当.
如：
We believe him to be guilty.我们相信他是有罪的.
At the meeting we elected him monitor.
What you said made Xiao Wang angry.
I found the classroom empty
He was seen to take his cap off.
We hear him singing in the hall.
He saw his face reflected in the water.
being locked 为动名词,往往在句中做主语,宾语,表语,定语,不作补语.

选A
spend some time on sth/ doing sth 花费时间做谋事,但 lock 在这里是用过去分词表示主语 I 在学习是很认真的。

B