Explanation: A video amplifier's main role in a display system, particularly one utilizing a Cathode Ray Tube (CRT), is to take the detected and processed composite video signal and boost its amplitude. This amplified signal is then applied to the cathode (or sometimes a control grid) of the CRT. By modulating the voltage on the cathode, the electron beam's intensity is controlled, which in turn varies the brightness of the pixels on the screen, forming the visible image. Option B (Resolver signals) refers to position sensing, unrelated to video display. Option C (Antenna X and Y signals) relates to antenna direction or specialized antenna types, not video amplification for display. Option D (Provide the drive signal to the sweep amplifier) is incorrect because sweep amplifiers are driven by horizontal and vertical synchronization circuits, not the video signal itself. The video amplifier handles image content, while sweep amplifiers handle beam positioning.