—Do you go to work by bus?
—________.
A．Yes，but I did B．No，but I do
C．No，but I used to D．No，but I didn’t
—Do you go to work by bus?
—________.
A．Yes，but I did B．No，but I do
C．No，but I used to D．No，but I didn’t
句意为：——你乘公共汽车上班吗？——不，但我以前常常乘公共汽车上班。used to do sth.过去常常做某事，此处省略了go to work by bus。
答案： C