你这个周末碰巧有空吗？

Are you free ___by ___any ___chance this weekend?

尼克，你碰巧看到我的钥匙了吗？

Nick, have you ___by ___any ___chance seen my keys?

碰巧你知道这个问题的答案吗？

___By ___any ___chance, do you know the answer to this question?