I saw him leave the office an hour ago . He at this time .
A. mustn''t be working
B. can''t be working
C. can''t work
D. may not being working
网友回答
A. mustn''t be working
(答案→)B. can''t be working
C. can''t work
D. may not being working
解析：must 表示猜测时只用于肯定句。may 可用于肯定句或否定句，但D项有明显错误。can 用于否定句中则表示“不可能”，本句的意义表示正在进行的动作，选C不合适。