don't worry,don't be nervous 为什么前面一个不用be?

don't worry,don't be nervous 为什么前面一个不用be? Don't be nervous Don't be nervous翻译 Don't be worried Don't worry don't worry be happy Don`t be worry 还是Don`t worry? don't be nervous ___ the teacher Don't be nervous .just r___ yourself. 为什么在be前面用don't Don't be worry...you'll be 别担心 Don't be worried Don't worry Don't worry about=Don't be worried吗