Economics, several courses of which I have taken thus far,()to be difficult but useful for almost all students。
A large crowd()expected at the football match。
MEDLINE光盘数据库的每一条记录大约是由26个字段组成的,其中又分为默认字 段和限制性字段两种,默认字段是指()
The school staff()gathered to hear the president speak。