Task: Question Answering
Input (English): When 1 gram of water is evaporated, the volume of the water vapor increases but the mass remains constant. Why does the mass of the water remain constant?  
 (A) The temperature of the water remains constant. (B) The pressure acting on the water remains constant. (C) The number of atoms in the water remains constant. (D) The distance between water molecules remains constant.
Output (English): C