it has been decided _when___they will leave for shanghai.
不可以用whether“是否”
it has not been decided __when__they will leave for shanghai
也可以用whether“是否”
it has not been decided __when__these foreign guests will visit our college
也可以用whether“是否”
这是主语从句, 不可以用if 引导
如不明白请追问,如果满意请采纳
手机提问者如果满意,请在客户端右上角评价点“满意”即可, 谢谢!
祝学习进步