Protecting the earth is not ____ to be left to the government.Everybody should be concerned.
The traditional goal of science is to discover how things are, not how they ought _____.
In their spare time, they will discuss the _____ to the study of English.
About _____ of the population of that country _____ on farms.
―Will you go to the Great Wall with us?―If John wants to go, _______
I was so angry that I felt like _________ something at him.