— Life now is not so easy as it ___________be, do you think so?

— Yes. I ___________ working seven days a week to get more pay.

A．used to; used to

B．was used to; used to

C．used to; am used to

D．was used to; am used to

均匀带电长直导线半径为1cm，线电荷密度为λ，其外部套有半径为2cm的导体圈筒，两者同轴。它们之间的电势差等于：（）

A.（λ／4πε）ln2

B.（λ／2πε）ln3

C.（λ／4πε）ln（1／2）

D.（λ／2πε）ln2