How Does Ultrasound Imaging of an Embryo Work

How does ultrasound imaging of an embryo work?

A) High-frequency light waves pass bounce off the embryo, and they are translated into a picture by a computer.
B) High-frequency sound waves bounce off the embryo, and they are translated into a picture by a computer.
C) Computer generated sound is passed through the embryo and an image is created.
D) Electrical pulses produced by the embryo are collected and translated into a picture by a computer.
E) Sound waves produced by the embryo are collected and translated into a picture by a computer.