Why can earthquakes be a warning sign that a volcanic eruption is about to happen?

An earthquake is essentially two tectonic plates rubbing against each other.
 normally, points where these two plates meet it where volcanos are formed therefore an earthquake could trigger the volcano by opening cracks where magma can seep through. 

Answerair masses develop near the equator are warm; tropical air mass

The correct answer is a)  a resource with a limited supply; it will run out.