What must every simple sentence contain?

Every simple sentence must contain two essential components:

1. Subject: The subject is the person, place, thing, or idea that the sentence is about. It tells us who or what is performing the action or being described.

2. Verb: The verb is the action word or state of being that describes what the subject is doing or being.

Let's see some examples:

* The dog barked. (Subject: "The dog," Verb: "barked")

* The sun shines brightly. (Subject: "The sun," Verb: "shines")

* She is happy. (Subject: "She," Verb: "is")

Note: While a simple sentence only *needs* a subject and a verb, it can also include other elements like objects, complements, and modifiers to provide more information.