john and his sister visit (their friends) (three times a year.)分别对括号提问.
问题描述：
john and his sister visit (their friends) (three times a year.)分别对括号提问.
答
Who do John and his sister visit three times a year?
How often do John and his sister visit their friends 第一题不用whom 吗可以用whom，但口语中常用who代替whom，如果前面有介词，一定是用WHOM