I_____frustrated when I wasn‘t sure of the coorect answer A.used _其他解答

I_____frustrated when I wasn‘t sure of the coorect answer A.used to B.used to be C.use to be

人气：488 ℃　时间：2020-01-28 20:40:26

解答

B used to be 过去常常...
句意是：
过去,当我不确定哪个是正确答案时我就很泄气.