it'll be cheap to travel everywhere by plane的形式主语和真正主语是、 并且希

it'll be cheap to travel everywhere by plane的形式主语和真正主语是、 并且希 It'll be cheap to travel everywhere by plane . It'll be chea It must be terrible to be grown up!这是形式主语,真正的主语to be grown u It'll be cheap___everywhere by plane.Atravel Bto travel Ctra it is one's duty to do sth.其中______是形式主语,真正的主语是______. 以it作形式主语,不定式作真正的主语,不定式to后面的动词可以是不及物动词吗? it 做形式主语 不定式做真正主语 不定式符号to可以省略的情况 It seems that 和 It seems as if中的是形式主语吧?真正的主语呢?逻辑主语呢?（请详细一点, It is +adj+ to do sth中It是形式主语吗?真正的主语是动词不定式to do st it is all right to show we're sad.这里面it做形式主语,真正主语是后面的不定式,但是 it作形式主语的问题it 作形式主语的句型是 it + be动词,还是it + 谓语动词? there be句型和it做形式主语形成的主语从句区别