#3 is the closest, but replace “less” with “fewer”. Whenever prices go up, customers buy fewer products. Products is countable, but product is not — so you could say: Whenever prices go up, customers buy less product.

1.Whenever prices goes up, customers buy less products. - nope 2.Whenever price goes up, customers buy less products. - nope 3.Whenever prices go up, customers buy less products. - ok . Why? You mean why not? 1. prices goes - does not agree (plural noun, singular verb) 2. (whenever price goes) - needs an article. - the price 3 - why? Agrees, works, correct . Homework?

I guess the third one is correct. because here prices refers to many products not just one product so we have to use it in plural form. then because prices is plural we have to use go instead of goes.