．安排5名歌手的演出顺序时，要求某名歌手不第一个出场，另一名歌手最后一个出场，不同的排法种数是         。（用数字作答）

  I was really anxious about you. You _______ have left home without a word.

A．mustn't

B．shouldn't

C．needn't

D．couldn't