Task: Question Answering
Input (English): Oil and gas are two sources of energy used in America. Which is the main reason oil and gas may be replaced with other sources of energy in the future?  
 (A) Oil and gas produce very little power. (B) Oil and gas work in too few machines. (C) Oil and gas are limited in their supplies. (D) Oil and gas are too costly to remove from the ground.
Output (English): C