Task: Question Answering
Input (English): A weather balloon is about 2 meters wide when it is near the ground. It grows to about 6 meters wide at higher altitudes. Which change most likely makes the balloon become wider at higher altitudes?  
 (A) More gases enter the balloon. (B) The gas inside the balloon gets much hotter. (C) The air pressure surrounding the balloon decreases. (D) Sunlight breaks down the material of the balloon.
Output (English): C