C. Sea horses are very unusual fish.
The word "fish" is a predicate nominative in letter C sentence. This is because a predicate nominative, also known as subject complement, is a noun or pronoun that follows a linking verb and renames the subject.
Sea horses - subject; are - verb; very unusual - adjectives; fish - predicate nominative.
A - Fish - subject
B - will fish - verb
D - fish - object
