ree college students did what theycould _____ the two children, although they was in danger

How many trees are there on topof the mountain? _________

How can I pass the exams，Mr Right—Well，you ________ a lot of hard work first.

The water and soil conservation project resulted infarmers ______ the crops on the farmland _____ trees and grass.

If you feel tired and sick of fat food, that is _______ you have to go to the hospital for a medical examination.