询问目的；询问原因why on earth?; why on earth?

• 你来干吗？

  Why have you come?

• 你干吗这样喊叫？

  Why on earth are you shouting like that?

• 他很能干，要不，干吗选他呢？

  He's very capable – if he wasn't, why on earth choose him?

• 他来管这事干吗？

  What does he think he's doing, getting involved in this?