A is mitosis because when a mitosis happen it always identical to the original cell it's like a clone.
And B is meiosis is different because when a mother have a child the child is not likely to look exact the same has the parent so they different.
Answer: Diseases are caused by a biological agent.
Germ theory of disease, the currently accepted theory of disease, says that many diseases are caused by microorganisms. These microorganisms are biological agents, too small to see without a microscope, they invade humans and animals to be able to grow and reproduce. These "Germs" can be protists, bacteria,fungi, viruses, prions, or viroids.
gas is more available and easy to get???
A polymorphic trait
I guess that's the closest I can get to answering because you didn't add enough details.