Concept:The cathode ray tube uses two pairs of deflecting plates to steer the electron beam in perpendicular directions.
Explanation:The X-plates are the pair of plates that create an electric field acting from left to right across the tube.
When a voltage is applied to the X-plates, this field pushes the electron beam sideways.
This sideways motion is along the horizontal axis on the screen.
The Y-plates, by contrast, deflect the beam up and down, which is vertical movement.
Thus, the specific function of the X-plates is to control horizontal deflection of the beam.
It does not reflect the beam, nor does it directly generate sinusoid waves.
Answer:A. deflect the electron beam horizontally