Because the speed of ultrasound in bone is about twice the speed in soft tissue, the distance to a structure that lies beyond a bone can be measured incorrectly. If a beam passes through of tissue, then of bone, and then another of tissue before echoing off a cyst and returning to the transducer, what is the difference between the true distance to the cyst and the distance that is measured by assuming the speed is always ? Compared with the measured distance, the structure is actually
(a) farther
(b) farther
(c) closer
(d) closer