A technician is using 5.0 MHz ultrasound to image a patient’s gallbladder. She sees two echoes, the first 78 μs after the ultrasound pulse is emitted and a second 136 μs after the pulse.

A. Distance to the first echo: 11.7 cm
B. Distance to the second echo: 20.4 cm
C. Distance traveled by ultrasound in 78 μs: 11.7 cm
D. Distance traveled by ultrasound in 136 μs: 20.4 cm