The correct answer is B) Each pump operating at a different pressure and discharging into a common line. This arrangement is hazardous because it can lead to backflow and potential ignition of flammable vapors. When two centrifugal pumps are discharging into a common line at different pressures, the higher pressure pump can force liquid back into the lower pressure pump, creating a risk of ignition and explosion. This violates basic safety principles for handling flammable cargoes. The other options are not as inherently hazardous. Option A is safer as both pumps operate at the same speed and take suction from a common line. Options C and D do not present the same pressure differential risks as option B.