Of grammar rules but the basic ones refer to sentence structure and parts of speech, which are noun, pronoun, verb, adjective, adverb, preposition and conjunction. Let’s look at the way sentences are put together and the words that form them.

Basic English Grammar Rules
Some of the most basic and important English grammar rules relate directly to sentence structure. Some of these rules specify that:
A singular subject needs a singular predicate.A sentence needs to express a complete thought.
Another term for a sentence is an independent clause.
Clauses, like any sentence, have a subject and predicate too. If a group of words does not have a subject and predicate, it is a phrase.If they can stand alone and make a complete thought, then they are independent and called sentences.If they do not express a complete thought, they are called "dependent clauses." An example of a dependent clause, which is not a sentence, is “when i finish my work”.
The correct answer is B (The safari stopped at an oasis, a moist, fertile spot in the desert) because an appositive can be a short or long combination of words that renames the noun.
