B.make sure
解析：for sure 是“无疑”的意思,通常放句尾 例子：The fighting was over for sure.战斗确实结束了.
be sure about+sth.后面通常不跟从句
make sure of +sth,理由同上 例子：Go and make sure of the place and time.去把时间和地点弄清楚.
因为题目中所缺的是动词短语,所以make sure +从句