Question

read the source of the allusion.
in one of aesops fables, a fox tries to reach a bunch of grapes. he cannot reach them and therefore cannot eat them, so he decides they must be sour.
what is the meaning of the allusion in the sentence below?
what zach said about your new bike is clearly a case of sour grapes.
pointing out important details that are hard to see
praising something that you admire and wish to have
finding fault with something that you cant have

Explanation:

The allusion "sour grapes" comes from Aesop's fables. In the fable, a fox can't reach grapes and decides they must be sour. When Zach says something is a case of sour grapes, it means he's finding fault with something he can't have. For example, if he can't have the new bike (maybe due to cost, unavailability etc.), instead of admitting he wants it and can't get it, he points out flaws (like pretending it's not good) which is similar to the fox devaluing the grapes he can't reach.

Answer:

finding fault with something that you can't have