Quantity A vs B of 3 consecutive integers?

Hey all, looking at problem #2 from PrepSwift Three Consecutive Integers I.

I got the answer wrong and the explanation isn’t making sense. I think I’m not understanding what Greg means by “Quantity,” but here was my train of thought:

a will always be smaller than c, therefore A/2 will always be < c.

Let’s try a couple of examples. One option is

First part of the explanation says:
3, 4, 5 where a= 3 and hence Quantity A becomes 1
b=1, that is, the two quantities are equal.

Not following that AT ALL. How did we get to 1?
(Correct answer is D FYI)

Remainder, not quotient.