have chance 和 have a chance 哪个 正确

have a chance 正确
have a chance
有机会；有希望
例句
1.We all have a chance of doing that.
我们每个人都有机会做到这一点.
2.Now they have a chance to prove it.
现在他们有机会证明这一点.
3.I finally have a chance to show off.
终于可以也让我表现一次了.