e used to do sth.是use的被动语态结构,“被用来做某事”.如：
The bamboo is used to make chairs.
be used to （doing） sth是“习惯于做某事”,to是介词,后面接名词或动名词.如：
She is used to the new life here.
She is used to getting up early evey morning.
used to do sth.是“（过去）常常做某事”,如：
I used to swim in a small river in my hometown.
used to do sth的否定形式和疑问形式有两种.以上题为例：
否定句：I usedn't to swim in a small river in my hometown.
I didn't use to swim in a small river in my hometown.
一般疑问句：Used you to swim in a small river in my hometown?(肯定回答：Yes,I used to.否定回答：No,I usedn't （to）.)
Did you use to swim in a small river in my hometown?（肯定回答：Yes,I did.否定回答：No,I didn't.)
题目“他过去在一家小店工作”,选C.