问题补充:
When he walks my desk, he often knocks my books the desk.
A. pass; off
B. past; off
C. pass; on
D. past; on
答案:
A. pass; off
(答案→)B. past; off
C. pass; on
D. past; on
解析:pass为动词,而第一空之前的词为动词,故选介词,所以将BC排除,knock sth on sth意思为用····敲···,为固定词组搭配。故选答案为B