ARDMS (American Registry for Diagnostic Medical Sonography) Practice Test

The correct answer is B. 3cm.

The depth of a reflector can be calculated using the formula d = ct/2, where d is the depth, c is the speed of sound in the medium (assumed to be 1,540 m/s in soft tissue), and t is the go-return time of the sound wave.

Given that the go-return time is 39 microseconds (or 39 × 10^-6 seconds), and the speed of sound is approximately 1,540 m/s, plugging these values into the formula gives us d = 1,540 × 39 × 10^-6 / 2 = 3cm.

Therefore, the reflector is 3cm deep.