Starting alphabet quartet

ABCD

Think of the first four symbols you’d sing when reciting the building blocks of language in order.

This clue plays on the word "quartet," which typically means a group of four. Here, it refers to the first four letters of the alphabet—A, B, C, and D—forming a simple sequence. The word "starting" hints at the beginning of the alphabet, making "ABCD" the straightforward answer. No hidden tricks, just a direct nod to the basics.