Which statement is true for single-celled organisms?
a.
they are often harmless.
b.
they always cause disease.
c.
they only live inside humans.
d.
they reproduce in a complicated process.

dogs is better and probably lizards.

humans can cause extinction of a species through overharvesting, pollution, habitat destruction, introduction of invasive species (such as new predators and food competitors), overhunting, and other influences. explosive, unsustainable human population growth is an essential cause of the extinction crisis.

explanation:

i didn't have the answer choices , but i tried my best.