Be sure __________ when you have time.

Be sure __________ when you have time.

A.of coming

B.about coming

C.to come

D.coming

答案及解析： C

解析：

be sure of／about sth. 对……确信／有把握；

be sure to do sth.表示一种期望、要求，意思为“务必……”“一定……”。