问题补充:
---------Where is Mr Li?
----------He in the office. I saw him leave just now.
A. must work
B. can’t be
C. might be
D. must be working
答案:
A. must work
(答案→)B. can’t be
C. might be
D. must be working
解析:must work必须工作;can’t be不可能……;might be可能; must be working肯定正在工作。句意:李先生在哪儿?根据下文,我看见他刚才离开了。可知前文指的是,他不肯能在办公室里面。故选B。