Temperatures in the winter drop because that part of the earth is tilted towardaway from the sun.

Away

Explanation:

During winter, the earth is tilted away from the sun. Due to tilting of earth away from the sun, the sun rays interact with the earth at shallow angle which causes the rays to spread more in the outward direction and thus the amount of heat energy that should reach planet earth at any given spot reduce.  

Also, the earth’s hemisphere which is tilted away from the sun have short days and long nights which prevents earth from heating and thus winter season occur.  

c

explanation:

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.