A. pressure and heat built up in the magma chamber
This is true as the pressure and heat built up is what cause the magma to be pushed out of the chamber through the vent. The higher temperature it is,the more it expands and the more likely it is to erupt.
B. plate tectonics and subduction
This is also true as volcanicity is caused by plate tectonics such as subduction. When the plate bends, cracks are formed which coul then be filled by magma and cause fissure eruption, afterwards forming volcanoes.
C. ground swelling and foreshocks
These are the consequences of volcanic eruption but not the causes and therefore is not true.
D. foreshocks and aftershocks
These are as well the consequences of volcanic activity like above and is not true.
As an Australian myself I can safely inform you that it is definitely Australia, despite the common misconception that the capital of Australia is Sydney or Melbourne.
