They became friends again that day. Until then, they _______ to each other for nearly two years.
Perseverance is a kind of quality --- and that’s ________ it takes to do anything well.
A heavy learning burden leads to unhealthy behaviors such as poor eating habits, which ___ damage the health of students.
How did you ___ to paint the whole house in a week?
Black clouds had completely ___ the sun.
It was an unpleasant subject ____ we _____ for a long time.