Prática CDL doubles and triples endorsement

You are pulling loaded doubles down a long grade. A coworker suggests using the trailer brakes alone to hold your speed so the tractor brakes stay cool. What does the CDL manual say?

• AGo slow enough that light use of all the brakes holds your speed.
• BUse the trailer brakes alone, since the trailers have more axles.
• CUse the trailer brakes alone, but on dry roads only.
• DSwitch between trailer brakes and engine brake every mile.