Already answered in pm ;P
Explanation:
A dichotomous key is a tool that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish. Keys consist of a series of choices that lead the user to the correct name of a given item. "Dichotomous" means "divided into two parts".
Saliva,unprotected intercourse,contact with infected blood (blood transfusion)
and women with an unborn child.
I can’t see the picture but it would be gravity going down