（1）used to do
否定形式：didn't use to do 或 usedn't to do
疑问形式：Did you use to do sth? Yes,I did.No,I didn't.
如：My brother used to go swimming in the sea. 我哥哥过去常常在海里游泳；
否定形式：My brother didn't use to go swimming in the sea.
疑问形式：Did your brother use to go swimming in the sea?
Yes,he did. No,he didn't.
（2）be used to doing
如：I am used to having a cup of tea in the morning.
我习惯于早上喝一杯茶。
