How To Say Good-Bye(句型篇)（一）

I have a meeting soon.
    I have an engagement soon.
    I have an engagement very shortly.
    I have a date very shortly.
    I think I'd better go now.
    I think I should go now.
    I think I ought to go now.
    I think I must go now.
    It's getting dark.
    It's getting dark outside.