I will correct myself, it's B and C.
I mistook A with B.

When they tell us in the question that Pool member A default HTTP monitor shows green it means the HTTP keep-alive monitor is attached to the member and is indicating that the member A is reachable through the keep-alive.
Pool member B indicates red which means it has the default HTTP monitor as stated, however it is indicating that it cannot be reached so the virtual server won't send traffic to there until it comes back up to green.
Pool member C says it does not monitor which means the color is blue and that a monitor is not attached to the pool member, so the virtual server cannot determine if it is up or down so it forwards traffic there.
Therefore the answer is pool member A and pool member C.

because when it is "blue" its health check is not verified , and any traffic that should be destined will be sent to th server. only red / black/ grey will not get traffic. black will still get persited traffic if its only just been manually disabled

why ?