– Is that man Mr. Green?
– It _____ be him. He has gone to Paris on business.
A:may
B:must
C:can't
D:shouldn't
在哈佛大学图书馆的墙上有一句名言:“此刻打盹,你将做梦;此刻学习,你将圆梦。”这句名言启示我们( )
在器官移植时,发生排斥不匹配的器官属于( )