1.eager--eagerly(副词作状语,修饰were waiting)
2.an--a(university是以辅音开头的)
3.All--Both(指代two American guests应用Both)
4.by--with(along with和…一道)
5.long--soon(As soon as一...就; As long as只要 )
6.followed--following(they发出follow的动作,故用现分作伴随状语)
7.there--which(there不能引导定从,介词后用which引导定从)
8.gave--would give(因为刚进入the lecture room 时还没有讲课,是将要讲课,故用过去将来时)