You are presented with the quiz "Global warming most threatens the Earth's ability to do 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 "global warming linked to human emissions of heat-trapping gases is changing the planet's climate". 

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


 

 Sustain life          