You can't imagine the hard time he had ______ the horse in.
Although many measures _____, the world’s economy is still going down.
The teacher asked the two students to discuss the question in a low voice______ they should bother the others.
One third of the country_____ covered with trees and the majority of the citizens______ black people.
Steve Jobs’ death _______ quickly and soon became the talk of the whole world.
It is the prevention of disease_____ its successful treatment that has led to the rapid increase of the world’s population.