Question: During a demonstration, a teacher pours CO_{2} gas over a candle, putting out the flame. Which physical property allows the teacher to pour the CO_{2} gas?

  Options: 
 A. The gas is more dense than the air.
 B. The gas is more visible than the air.
 C. The gas smells different from the air.
 D. The gas evaporates faster than the air.
Answer: A