I think you have a problem. 我觉得你有问题。

　　I don't think it's a good idea to leave now. 我觉得现在离开并不是个好主意。

　　I don't think we're met before. 我觉得我们之前没有见过面。

　　I think that my math teacher is an asshole.  我觉得我的数学老师是个混蛋。

　　What makes you think so? 你为什么会那么想？