Without the specific passage to refer to, I can't provide a definitive answer. However, otters are known to be primarily carnivorous, eating a diet that consists mainly of fish, crustaceans, and small mammals. Some species of otters may also consume plant matter occasionally, but they are predominantly classified as meat-eaters.
If it's accurate to say that otters eat both plants and meat in varying degrees, the best inference would be:
D are both plant-eaters and meat-eaters.
If the passage focuses primarily on their consumption of meat, then:
A are meat-eaters.
For an accurate choice, please provide the relevant passage.