Since the main purpose of learning Chinese language is to communicate with Chinese people more fluently, the learners need to understand and use more oral expressions which are frequently used in daily communication. For example, the phrase 不好说is to show to be uncertain of or have no confidence about what has said. You may often hear it in the dialogue as follow. A: 天阴得这么厉害，你说会不会下雪呀？B：那可不好说.
Another common phrase should be 不好意思which is to show apology for the inconveniences that the speaker has brought or possibility has brought. As a matter of fact, you can apply it in the situations that you are showing apology for what you have done to others. 不会吧is also important for the overseas students who learn Chinese language to know because it is to distrust what the other party said like 不会吧，他是那么老实的一个人.
If what the other party said is terrible, it means the speaker does not hope it becomes true. However, if the case is good, it means the speaker feels joyful and cannot believe that it is true. Sometimes, it is used to emphasize what the other party said is impossible. For instance, A: 那边那个男生说想请你做他的舞伴. B:不会吧？你说的是那个帅哥？The phrase 不敢当is often applied to show that the speaker can’t accept the granted title or treatment like 那可不敢当，您比我岁数大。还是您先请吧.
If you hear Chinese people say 不得了了, you should know there must be something serious happen because it is applied to mean the case is serious like 不得了了，工地砸伤人了！The teachers may also tell you the meaning and application of 不对呀when they teach Mandarin language. It is used to notice or doubt some abnormal cases. Usually it is followed by some cases that are noticed or doubted. You can make sentence like 不对呀，都上课了了，怎么一个人也没有哇？