Which is a Compound Sentence?

A compound sentence is a sentence that has two INDEPENDENT clauses that are joined by a comma.

Explanation:

An independent clause is a statement that can stand alone as a sentence. But when two independent clauses are conjoined, then the sentence would be considered a compound sentence.

Example: "The backyard is vast, and so is the front yard."

Both statements can be used in their own sentence, "The backyard is vast," and, "So is the front yard," can both be their own separate sentences