You are presented with the quiz "If a planet cannot sustain life, then the planet may be too close to what?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "if a planet becomes too hot then that planet cannot sustain life" and "if a planet is too close to a star, then it will be too hot for liquid water to exist". 

So, what's the best answer to the question?


 

        a star   