The correct answer is - a. The formation of a mountain range.
When there's a geologic activity that is pushing the crust up, or rather lifting up the area, we have the process of formation of a mountain range. This type of activity is usually as a result of two continental tectonic plates colliding with each other, thus creating enormous pressure on the crust, which in turn makes the crust go up and gain on elevation, eventually creating a mountain range.
Nice examples for this type of activity are the Himalayas, created by the collision of the Indian plate and the Eurasian plate, the Andes, created by the collision of the Nazca plate with the South American plate, or the Atlas Mountains, created by the collision of the African and Eurasian plates.
