“ used to 加不定式”表示过去常常干某事，现在不在干了。例如 :
I used to go to work by bus. Now I take a taxi.
She used to be very shy.
“ be used to doing ”表示习惯于干某事。
【例如】
I am used to getting up early and going to bed early.
He is used to being praised by others.
关系从句中的谓语动词
在“ one of + 名词 ( 复数 )+ 关系从句”中的单复数在“ one of+ 名词 ( 复数 )+ 关系从句”中，关系从句中的谓语动词常采用复数形式。
【例如】 She is one of the students who have passed Band Six.
This is one of the best books that have been published recently.
one 之前有 the only 等修饰语时从句动词要用单数。
【例如】 She is the only one of the girls who is chosen as the member of student union.
He was the only one of the boys who was given a prize.
以 only 引导状语位于句首引起的倒装
Only by shouting at the top of his voice was he able to make himself heard. Only in this way can we achieve what we want.Only in each afternoon does the university library open. Only under special circumstances ____to take make up tests. (CET-4 1997,6)
A) are freshmen permitted
B) permitted are freshmen
C) freshmen are permitted
D) are permitted freshmen
Only 加状语位于句首，句子用倒装语序，故答案为 A 。