Final answer:
A group of morphemes forms a phrase, which is a unit within a sentence functioning without including both a subject and a verb. Syntax is the set of principles that govern sentence structure but is not a group of morphemes itself.
Step-by-step explanation:
A group of morphemes would correspond to the choice, D. phrase. A morpheme is the smallest grammatical unit in a language that carries meaning. It could be a word, or part of a word such as a prefix. When morphemes are combined, they form words, and when words are combined without including both a subject and a verb, they form what is known as a phrase. Phrases function as a unit within a sentence but do not contain both a subject and a verb, which distinguishes them from clauses. Syntax, on the other hand, is the set of rules, principles, and processes that govern the structure of sentences in a given language. This includes word order and how phrases and clauses are put together.
As for the other options, a sentence is a set of words that is complete in itself, typically containing a subject and predicate, conveying a statement, question, exclamation, or command. A syllogism is a form of reasoning in which a conclusion is drawn from two given or assumed propositions (premises), each of which shares a term with the conclusion and shares a common or middle term not present in the conclusion.