What are the three core parts of a simple sentence?

The three core parts of a simple sentence are:

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

2. Verb: The action or state of being that the subject is doing or experiencing.

3. Object: The person, place, thing, or idea that is directly affected by the verb. This is optional; some sentences don't have an object.

Here's a simple example:

* Subject: The cat

* Verb: sat

* Object: on the mat

The cat sat on the mat.