A, because all the other are in direct reference to something
The answer i believe is "what"
It might be clearer to say: According to the dictionary, a squawk is not the same thing as a squeak. there's no need for them to be plural in your sentence and it's likely that, in the dictionary, they're listed as "squeak" and "squawk" singularly. when describing dictionary definitions it's best to use the form of the word that the dictionary uses for clarity.
I think the answer is B, C, D but im not sure
