Answer:
I believe it is cardiovascular since they all involve the heart
You can tell by Crying... If the baby is in very serious pain she / he will scream and not stop until releive if the baby is in very little to no she/he will just make very fant sounds and you kind of can sens when a baby is in pain ...
D,it never acceptable to ignore rules or etiquette but A, when no one else notices you ignored the rules.