The function of a proportioning control valve (PCV) in a brake system is to

ensure that equal pressure is supplied to the front and rear brakes throughout every braking operation

reduce the brake fluid pressure when the brakes approach their lockup point

cause less brake fluid pressure to act on the front brakes than on the rear brakes when the fluid pressure exceeds a predetermined level

cause less brake fluid pressure to act on the rear brakes than on the front brakes when the fluid pressure exceeds a predetermined level

overheating of the fluid due to frequent brake application

over-cooling of the brakes during high speed driving

keeping the vehicle without use for an extended period

an excessively high engine speed on a downhill road

brakes function more effectively

brakes fail completely

brake operation is delayed after depression of the brake pedal

vapour locking has no effect on brake performance

lubrication

power transmission

cooling

none of these

a high boiling point

low viscosity

compatibility with rubber and metal parts

all of these