When pressure is kept constant, a gas causes it to expand.
a. cooling
b. heating
c. maintaining the temperature of

When pressure is kept constant, heating a gas causes it to expand. The correct option among all the options given in the question is option "B". When the pressure is kept constant and heating is done to the container containing the gas, then the molecules of the gas start hitting the walls of the container at a faster rate. The kinetic energy of the molecules increases. This makes the gas to expand.

Ihave no idea sorry