How are the respiratory and circulatory systems connected?
a. they communicate using neuroendocrine cells
b. they connect across synapses
c. they trade oxygen and carbon dioxide
d. they send hormones to each other

 C.  They trade oxygen and carbon dioxide.

fumikage isn't really a bird, and tsuyu does have teeth. tsuyu has a transformation quirk which still allows her to be partially human. otherwise we'd have a large frog running around. fumikage has teeth because again, he isn't a bird. his head was a quirk mixture if i'm correct.