Question

select the best detail to show that humans have bacteria on their skin.
bacteria are the smallest life forms on earth. they are made up of just a single cell and are so tiny that 1,000 of them would fit on the period at the end of this sentence. they’re everywhere—on land, in water, even inside you. and there may be hundreds of thousands more to be discovered, including in the harshest environments on earth—hot springs, sea vents, and areas deep beneath the soil.
from rochelle strauss, tree of life: the incredible biodiversity of life on earth. copyright 2004 by kids can press

Explanation:

To show humans have bacteria on their skin, we need a detail directly related to bacteria on human skin. The sentence "They're everywhere—on land, in water, even inside you" includes that bacteria are on or in humans (and "inside you" implies on skin too as a boundary), while the other details are about bacteria's size and undiscovered habitats, not specifically skin. So the relevant detail is "They're everywhere—on land, in water, even inside you."

Answer:

They're everywhere—on land, in water, even inside you.