为什么写成be at home

为什么be in=be at home He must be at home.为什么用be? at home be He can't be at home.为什么在at前面有be?什么情况下要加Be? I have to be home by ten o'clock.为什么不是be at home? He stayed at home 写成现在时 be home和at home区别 be home和at home的区别 You must be home at . It will be at home you must be home at at home不是动词词组吗 为什么前面用be动词 例如He is not at home.