1“There is no reason to be”中to be的用法

1“There is no reason to be”中to be的用法
2像sit,wait 延续性动词加时间后面必须跟for吗
3be off是否带有未来之意
4”It's rude to talk with your mouth full of food"什么情况下名词后可以跟形容词作定语
5__is a good way of excise for both young and old A.Walk B.Walking
6是there has been还是there have been
7“leave sth.+地点”地点前必要时要加介词吗
8make a living有没有复数形式
5名词不可以做主语吗