The following statement is a simple sentence, for it contains but one subject and one predicate.
1. The polar bear | lives in the Arctic regions.
The framework or skeleton of this simple sentence consists of the subject noun bear (the simple subject) and the predicate verb lives (the simple predicate). To make the complete subject, bear takes as modifiers the two adjectives the and polar and to make the complete predicate, lives takes as modifier the adverbial phrase in the Arctic regions.
By attaching another simple subject to bear we make a compound subject. Similarly, we make a compound predicate by adding another verb.
2. The polar bear and the walrus | live and thrive in the Arctic regions.
The compound subject is bear and walrus; the compound predicate is live and thrive. Both verbs are modified by the adverbial phrase in the Arctic regions. The sentence itself is still a simple sentence.
In each of the following simple sentences either the subject or the predicate or both are compound.
3. Games and carols closed the busy day. - Rogers.
4. The stars leap forth, and tremble, and retire before the advancing moon. - George Meredith.
5. Madame Defarge knitted with nimble fingers and steady eyebrows and saw nothing. - Dickens.
6. Work or worry had left its traces upon his thin, yellow face. - Doyle.
7. Crows flutter about the towers and perch on every weathercock. - Irving.
8. He gained the door to the landing, pulled it open, and rushed forth. - Lytton.
9. Countrymen, butchers, drovers, hawkers, boys, thieves, idlers, and vagabonds of every low grade, were mingled together in a dense mass. - Dickens.
10. There stood the broad-wheeled wains and the antique plows and the harrows. - Longfellow.
11. Both Augustus and Peters joined with him in his design and insisted upon its immediately being carried into effect. - Poe.
12. Women and children, from garrets alike and cellars, through infinite London, look down or look up with loving eyes upon our gay ribbons and our martial laurels. - De Quincey.