Technician a Says That a Too-Rich Air-Fuel Mixture Can Be

Technician A says that a too-rich air-fuel mixture can be caused by a defective fuel pressure regulator. Technician B says that a defective fuel pressure regulator can cause a too-lean air-fuel mixture. Which technician is correct?

A) Technician A only
B) Technician B only
C) Both technicians A and B
D) Neither technician A nor B