What radar display changes indicate the correct approach to a SART?

The correct answer accurately reflects how a Search and Rescue Transponder (SART) appears on a radar display and what the information signifies for a rescuing vessel. When a SART is activated, it transmits a signal that appears as a series of dots on a radar screen that indicates its position. As a rescue vessel approaches the SART, the dots start to form increasing arcs, which visually represents that the rescuing vessel is closing the distance to the SART.

In this context, reducing speed as the arcs get greater in degree is an essential aspect of safe navigation. As a vessel approaches a distress situation, it is crucial to slow down to maintain control and ensure safety for both the rescuing crew and those in distress. This reduced speed allows for a careful assessment of the situation and helps to avoid collisions or accidents, particularly in potentially hazardous or crowded water conditions.

The other answer choices do not accurately describe the display behavior or the appropriate action for the rescuing vessels. The confusion around the details in the other options can lead to misunderstandings about radar operation and safe rescue procedures, which emphasizes the correctness of the right interpretation provided in the choice discussed.