The ultra sound waves coming from the transmitter pass through the body and once they hit a boundary (the baby) they are partially reflected back to the transmitter and the image appears on the screen. The longer the time taken is to reflect, the further away it is, so darker/lighter on the picture.
Cells Come from other living things
The answer should be Fertile Crescent.
Hope this helps!
C. it determines which protein molecules to synthesize.