A：

Ultrasound A represents signals of liver tissue collected by sensor at a single time point. So, it is a line. Place a transducer that produces ultrasound pulses on one point of body surface. Sound beams are sent into the body and the signal amplitude returned from the interface of tissue is shown on the screen. The Y-axis indicates the propagation duration of ultrasound, i.e. detection depth while the X-axis represents the amplitude of echo pulse. Therefore, acquire the information on thickness of organ as well as depth and size of focus according to echo locations reflected by ultrasound from probe (transducer). It is also possible to conduct certain qualitative analysis of focus in light of other features of echo, including amplitude and density.