According to 46 CFR §56.07-10, a relief valve protecting a piping system must have sufficient relieving capacity to prevent system pressure from rising more than what percentage above the maximum allowable working pressure?

Why C is correct

46 CFR §56.07-10(b)(2) requires that the relieving capacity of a relief valve be sufficient to prevent pressure from rising more than 20 percent above the system maximum allowable working pressure. The 120 percent set-pressure certification requirement for the valve's rated capacity is a related but distinct requirement in the same paragraph.