The correct answer is b. B only.
Technician B is correct in their description of a fixed caliper. A fixed caliper does indeed use pistons on both sides of the brake disc to apply pressure to the brake pads. This design allows for more even and consistent braking force distribution.
On the other hand, Technician A's description of a floating caliper is not entirely accurate. A floating caliper typically uses hydraulic pressure to push one side of the caliper, which in turn squeezes the brake pad against the disc.
The caliper then slides or "floats" on a mount to apply pressure to the other pad through a lever action. So, while hydraulic pressure is involved, it is not part hydraulic and part lever action as described by Technician A. Therefore, the correct answer is b. B only.