Epitome of simplicity

ABC

Think of the first three things you learn when mastering the basics of almost any written language.

Epitome of simplicity" hints at the most basic or fundamental example of something easy to understand. In this case, it’s playing on the idea that the alphabet starts with the simplest building blocks—letters—and the first three letters, A, B, and C, represent the absolute basics. The answer, 'ABC,' is a straightforward nod to that concept, making it a perfect fit for the clue.