Here's why:
* Compound sentences are made up of two or more independent clauses joined by a coordinating conjunction (like "and", "but", "or", "so").
* Each independent clause has its own subject and verb.
Example:
"The sun is shining, and the birds are singing."
* Independent clause 1: "The sun is shining" (subject: sun, verb: is shining)
* Independent clause 2: "the birds are singing" (subject: birds, verb: are singing)
Therefore, a compound sentence has at least two subjects and two verbs.