Not able to understand why c is the correct answer like, d can also be the answer

GRE Quant Problem Solving
1
  1. If a and b are integers such that a > b > 1, which of the following cannot
    be a multiple of either a or b?
    (A) a – 1
    (B) b + 1
    (C) b – 1
    (D) a + b
    (E) ab

For this if I take a=3 and b=2 and a=4 and b=3 then the answer will be d but solution says it is c, like how?

2

What if a = 3 and b = 1?

3

b cant be 1 tho

4

B cannot be 1 as it has to be more than 1, mentioned in the question

5

Sorry, I missed that. Try a = 8 and b = 2. a + b = 10, which is a multiple of b.

6

That’s what I’m saying different numbers are giving different answers, so how can I choose the correct one

7

It’s cannot → must not. If you can find a number that works with a certain option, cross it out.

This won’t be the case for C.