Explanation: STC stands for Sensitivity Time Control (or Swept Gain Control). It is a crucial feature in RADAR receivers. The purpose of STC is to reduce the effect of strong, unwanted echoes from close-in targets, such as sea return (reflections from ocean waves) or ground clutter. RADAR signals reflect much more strongly from nearby objects than from distant ones. Without STC, these powerful close-range reflections can overload the receiver, making it impossible to detect weaker, more distant targets. STC works by automatically reducing the receiver's gain immediately after the transmit pulse, then gradually increasing the gain over time. This effectively "desensitizes" the receiver to strong, nearby clutter while maintaining sensitivity for more distant targets. Therefore, STC directly addresses and mitigates the problem of strong near-field echoes like sea return. * **A) Increase receiver stability:** STC does not primarily affect frequency or amplitude stability. * **B) Increase receiver sensitivity:** STC actually *decreases* sensitivity for close-range targets to prevent overload; it doesn't generally increase it. * **C) Increase receiver selectivity:** Selectivity relates to distinguishing between signals of different frequencies, while STC operates in the time domain, affecting gain based on distance/time.