根据超声成像的基本原理，当超声波在某生物组织中的传播速度为1540 m·s-1，接收一个脉冲回波的所用时间为0.02ms，则产生该回波的生物组织的深度是（ ） According to the basic principle of ultrasound imaging, when the propagation velocity of ultrasound in a biological tissue is 1540 m·s-1 and the time taken to receive a pulse echo is 0.02 ms, the depth of the biological tissue that generates the echo is A、1.54m B、1.54cm C、3.08m D、3.08cm