Why is it difficult to identify the cause of many nervous system disorders?
the genes associated with the diseases are not known.
there are no obvious defects in brain structure.
the onset and display of symptoms varies between patients.
all of the above

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.

the missing space is phylum