Final answer:
The word group is a complete sentence because it has both a subject and a predicate, forming a complete thought.
Step-by-step explanation:
The word group "Ruminants are animals that chew their cud" constitutes a sentence. This word group has a subject (“Ruminants”) and a predicate (“that chew their cud”), making it a complete thought which is characteristic of a sentence. Therefore, the correct answer to the question, whether this word group is a sentence or a clause fragment, is “O Sentence”.
In linguistics and grammar, a sentence is a linguistic expression, such as the English example "The quick brown fox jumps over the lazy dog." In traditional grammar it is typically defined as a string of words that expresses a complete thought, or as a unit consisting of a subject and predicate.
In non-functional linguistics it is typically defined as a maximal unit of syntactic structure such as a constituent. In functional linguistics, it is defined as a unit of written texts delimited by graphological features such as upper-case letters and markers such as periods, question marks, and exclamation marks.