have to

• 他的病很重，非得马上送医院不可。

  He's seriously ill and must go to the hospital immediately.

• 棉花长了蚜虫，非得打药不成。

  The cotton has aphids and must be treated with insecticide.

• 干这活儿非得胆子大。

  This job's not for the faint-hearted.