Answer: Technician A is correct.
Explanation: An open ground on the right may be the reason the headlight is not functioning on low or high beam. Most electrical circuit related problems in automotive are caused by open ground.
A ground should be clean, tight and free of corrosion and also making good metal to metal contact.
A ground is an electrical circuit system or connection in an automotive.
A dimmer switch on the other hand is a device that controls the vehicle's headlight functions. If the headlight does not function on high or low on the right. It can't be a dimmer switch, hence it may be ground problem.