In a further experiment, the researchers add a compound to the cell growth medium that both binds and releases protons (h+) and also passes through lipid membranes.

the answer is

c. parental

the correct answer is 4) heat and pressure

metamorphic rocks arise from transformation of existing rocks types, in a process called metamorphism. during metamorphism the original rock(prolith) change into metamorphic rock by heating (150-200c) and pressure of more than 1000 bar. the original rock can be sedimentary, igneous, or existing metamorphic rock.