The answer is B. Well it's the best answer.
The correct answer is "absolute temperature".
In fact, Charle's law states that, for a fixed amount of gas kept at constant pressure, the ratio between the volume of the gas V and its absolute temperature T is constant:

And this equation can be also read as: when V changes, T changes by the same proportion, so this means that the volume V is directly proportional to the absolute temperature T of the gas.
The ratio of the distance a bullet travels to the amount of time it takes to travel is known as the speed or velocity of the bullet, depending on whether we need to know the direction or not. Speed is a scalar quantity. It describes to "how fast an object is moving", in our case how fast the bullet is moving.Velocity is a vector quantity. velocity describes "the rate at which an object changes its position".