The correct answer is
D. It has a strong influence on the ecosystem.
Step-by-step explanation:
Keystone species are organism that define an entire ecosystem. Without the presence of keystone species, the ecosystem would be totally different and it will cease to exist. If keystone species disappear from the ecosystem, no other species would be able to fill its ecological presence. Some keystone species are Sea Otter. Sea Stars and Large Mammalian Predators.