A：Are you free tonight?
你今晚有空吗?
A：I think so.
我想有吧。
注释：
a.free a. 有空的
= available
Are you free now?
= Are you available now?
= Are you off now?
(你现在有空吗?)
b.I think so.我想是吧。
I don't think so.
我想不是吧。/我不这么认为。
A: Is she beautiful?
(甲：她美吗?)
B: No, I don't think so.
(乙：不，我不这么认为。)