Answer:
The correct answer is synecdoche.
Step-by-step explanation:
Onomatopoeia is not the answer. Onomatopoeia refers to words that represent a sound by imitating it, such as bang, crash, click, buzz etc.
Synecdoche is a type of figurative language that uses a part of a whole to represent the whole. In the sentence we are analyzing here, the speaker mentions the ABC's. As we know, the ABC's refers to the alphabet. A, B, and C are the first three letters of the alphabet, which is constituted of 26 letters total. Therefore, when we say "ABC's", we are using a part - the first three letters - to refer to the whole - the complete alphabet with 26 letters. What we have is synecdoche.