The choices can be found elsewhere and as follows:
a. Increased temperature and pressure
b. Melting and crystallization
c. Exposure and weathering
d. All of the above
I believe the correct answer is option C. It would be Exposure and weathering that would cause an igneous rock to become soil. Weathering breaks rock down into small particles which are carried away by erosion and deposited somewhere, sometimes creating very verdant soils.