Task: Question Answering
Input (English): A light bulb manufacturer claims its light bulb is "twice as bright" per unit of electrical energy consumed as the leading light bulb. If this claim is correct, what factor must be accurately compared between the two bulbs?  
 (A) how much each bulb weighs (B) how long each bulb lasts (C) how much heat each bulb releases (D) how much metal each bulb contains
Output (English): C