一个英语题目—Dad, can I surf the Internet? —Again? I wish that you

一个英语题目
—Dad, can I surf the Internet?
—Again? I wish that you ______ going on line ______ your health.
A. know; will do harm to B. knew; are doing harm to
C. know; have done harm to D. knew; were doing harm to
这个英语题目为什么答案是B啊
要不要把B的选项are 改成 is 啊，因为going on line 是动名词做主语啊，应该用单数啊