A．that
连词that本身没有意义，在从句中不担任任何句子成分，在宾语从句中有时可省略。
I hear (that) he has joined the football club. 我听说他已经加入了足球俱乐部。
That light travels in straight line is known to all. 众所周知，光是以直线传播的。
It so happens that I know the man. 碰巧我认识那个。
Is it certain that they will win 他们一定会赢吗
