can be和must be should be的区别

can be是指可能会,可能是,表示可能性
例：That can't be true.那不可能是真的.
must be指一定会,准是,一定是,表不可避免性,必然会,必定会.
例：He must be there by now.他现在一定在那里了.
should be是指应该是,应当是
例：They should be there by now.他们现在应该已经到那了.