The answer to this question would be D, gaviotas, because the meaning of gaviotas is "seagull, which is a kind of bird, Las ___________ son aves que viven en las regiones costeras, in English would be "The ----- are birds that live in coastal regions"
so with the answer, and in English it would be "The seagulls are birds that live in coastal regions"
and in Spanish it would be " Las gaviotas son aves que viven en las regiones costeras".
Hopefully this is helpful and correct. (:
Con suerte, esto es útil y correcto. (:
