D. both B and C will cause gas pressure to decrease because adding more gas is like adding more energy and reducing the space (volume) the atoms will move more quickly but won't have space, therefore pressure will increase.
Here, it can be seen that if the volume of the container decreases then the pressure will increase.
If the volume of the gas increases without changing the dimensions of the container then the pressure will increase. More amount of gas in the same volume will increase pressure.
Understanding Newtons second law that everything has an equal and opposite reaction. The reaction force from a balloons air being pushed out is the preasurized air it had to push out into the open air.
