Trees are very important to our environment. They can _____ wind from blowing the earth away.

With drink and food ________, the prisoner had to walk out of the cave where he was hiding．

I think you’ve get to the point ______ a change is needed, otherwise you’ll fail.

My father is ill in hospital, I’m looking after him. —___________.

Everyone kept silent and tried to come up with an idea to _________ this problem.