Which statement is true regarding keystone species in an environment?

The question is not complete, the options are not given.

But the correct answer is.

They are likely symbiotic with the dorminant species.

Explanation:

A keystone species is a species which has disproportionately large effect on the communities it hold together by maintaining the biodiversity of the ecosystem and causing the abundance of other organisms present in the ecosystem. They play a role in the existence of species present in their environment.

The tree types of keystone species are predators, mutualist and ecosystem engineers.

i believe the correct answer is d

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."