What are the two major types of sonar?

The two major types of sonar are active and passive, making the correct choice C.

Active sonar works by emitting sound pulses into the water and listening for echoes that bounce back from objects, such as submarines or the seafloor. This method helps in detecting, locating, and identifying targets underwater. It is commonly used in applications such as navigation, surveying, and object detection, providing a proactive approach to sensing the marine environment.

On the other hand, passive sonar does not emit sound pulses; instead, it involves listening for sounds made by other objects in the water, such as the noise from a vessel's engines or marine life. This method is covert and essentially a surveillance technique that allows for detection without revealing the position of the sonar system itself. It is widely utilized for tracking and gathering intelligence.

The combination of these two sonar types covers a wide range of underwater monitoring needs, enhancing the effectiveness of naval operations and marine research.