An Ideal Gas Is Slowly Expanding to Twice Its Original $\sqrt { 2 }$

An ideal gas is slowly expanding to twice its original volume with no change in temperature. The average speed of the molecules in the sample is

A) increasing by a factor of 2.
B) increasing by a factor of $\sqrt { 2 }$
C) staying unchanged.
D) decreasing by a factor of $\sqrt { 2 }$
E) decreasing by a factor of 2.