To Account for the Fact That the Volume of a Gas

To account for the fact that the volume of a gas is directly proportional to its temperature in kelvins, it is necessary to postulate that:

A) There is a distribution of molecular speeds between gas molecules
B) The molecules have negligibly small volumes
C) Molecules collide with each other
D) On the average, molecules move faster at higher temperatures
E) None of these explain this direct proportionality