It is necessary that everything be ready by three o'clock.在台灣的高中，很多英
文老師會把這句話解釋成"should"被省略。30年前，台北有位高中補教名師鄭蓉就告訴學
生，他問了well-educated American，結果對方說，不是省略should，是根本就沒有
should。這種用法是present subjunctive!
It is necessary that everything be ready by three o'clock.(Ammerican usage)
It is necessary that everything should be ready by three o'clock.(British
usage)