The correct answer is (a) Radio detection and ranging.
RADAR is an acronym for Radio Detection and Ranging. It is a system that uses radio waves to detect and locate objects. RADAR works by emitting a beam of radio waves and then measuring the time it takes for the waves to bounce off an object and return to the source. This information can be used to calculate the distance, speed, and direction of the object.
RADAR is used in a variety of applications, including air traffic control, weather forecasting, and military surveillance. It is also used in some consumer products, such as radar detectors and parking sensors.
(b) Radio divergence and ranging is not a correct answer because it does not accurately describe the function of RADAR. RADAR does not measure divergence, which is the spreading out of a beam of light or other radiation.
(c) Radio detection and radiation is not a correct answer because it does not accurately describe the function of RADAR. RADAR does not detect radiation, which is the emission of energy in the form of waves or particles.
(d) Radial distance and ranging is not a correct answer because it does not accurately describe the function of RADAR. RADAR does not measure radial distance, which is the distance from a point to a line or curve.