The correct answer is letter C
Metamorphism comprises a series of processes that take place inside the earth's crust and that cause mineralogical, chemical and structural changes in preexisting rocks when subjected to different physical-chemical conditions from those that originated them.
Metamorphic rocks owe their characteristics to several factors, the most important of which are: the composition of pre-existing rocks that experience metamorphism phenomena, temperature and pressure during the metamorphism process, and the effects of the circulation fluids.
During the processes of metamorphism, in general, the addition of new chemical elements or compounds does not occur. However, the mineralogical composition of metamorphic rocks is conditioned by the chemical composition of pre-existing rocks.
For example, many metamorphic rocks have a high silica content, which indicates that pre-existing rocks were also rich in silica.
A metamorphized basaltic rock can present in the new minerals, as a whole, about 50% silica and percentages of iron, magnesium, calcium and aluminum oxides resulting from the previous rock.