in the storybook that he had bought not long before the boy didn’t notice his mother go

问题补充：

in the storybook that he had bought not long before, the boy didn’t notice his mother go into his room.

A Losing

B. Lost

C. Having lost

D. To be lost

答案：

解析： 考查非谓语动词做状语.现在分词表示正在进行的动作,故去分词表示发生过的,被动的动作,不定式表示将要发生的动作.完成时表示已完成的动作.根据题意,可知这个男孩是lost的对象,迷失的,故选B,沉迷在故事书中.