Max NS224 shelves is 4, but max stack size is 1. Also, max number of direct attached NS224 shelves on the A400 is 2. Any more than that would have to be switch attached. Option A is definitely wrong because you can't daisy chain the shelves. Option B is ambiguous because it doesn't specify whether the existing 3232C switches are dedicated switches for the existing two NS224C shelves, or are the cluster switches. If they are dedicated storage switches the new shelves could be attached to them. If they are the cluster switches, they cannot be (in ONTAP 9.8). Option C is correct. Option D could be correct if the existing two shelves are directly connected. So options B, C, and D could all be correct, but I'm going to guess they want you to choose CD.