Answer the following question given this paragraph: 

Various studies were done on the effects of temperature changes on both pressure and volume by two prominent French scientists, Jacques Charles (1746-1823) and Joseph Louis Gay-Lussac (1778-1850). In 1802, Charles and Gay-Lussac both proposed that for a fixed amount of gas at a constant pressure, the volume is directly proportional to its absolute temperature (V ∝ T). Figure below illustrates the volume-temperature relationship.


Q: In 1802, charles and gay-lussac both proposed that for a fixed amount of gas at a constant pressure, what is directly proportional to its absolute temperature?

 Choices:

- air

- liquid

- density

- volume

A:
volume
