Question: An enclosed 20 mL metal cylinder was filled with a gas sample at room temperature. The sample then was transferred to an empty 40 mL enclosed container, also at room temperature. After being transferred, the volume of the gas was

  Options: 
 A. 10 mL.
 B. 20 mL.
 C. 30 mL.
 D. 40 mL.
Answer: D