C. 20 because 39-19 is 20 so there are 20 neutrons and the atomic number is the same as number of protons and electrons.
B.AGUCCGUUA I hope this helps you out
D. It provides buoyancy to a fish.
This air pocket is known as the swim bladder, and also called air bladder. This is a buoyancy organ possessed by most bony fish. The air bladder is located in the body cavity and is derived from an out pocketing of the digestive tube.
