情态动词往往表达说话人对有关行为和事物的态度和看法,认为可能,应该,必要等.如must,can(could),may (might),need等等.
must be是两个词,应当分开来看.must 意为一定,必须,是情态动词,后面跟动词原形,be是系动词.当must后要跟名词或形容词时,就应当加上be.
例如：He must be a teacher.
That must be a wonderful movie.
Michael must be strong enough to overcome all the difficulties.