The combined gas law states that
PV
T
= C, where P, V, and T are the pressure, volume, and temperature of a gas, and C is a constant.

Avogadro's Law says that the constant C is directly proportional to the amount of gas, n (moles), where the proportionality factor R is the universal gas constant. So, C = nR.

From these two laws we can derive the Ideal Gas Law, which is
A) P = VnRT
B) PV = nRT.
C) P = V/nRT
D) PV = nR/T