Organ system. The blood vessels, blood, and the heart are organs which work together to form the circulatory system.
Ask the vet. They should have a solution to the problem or advise you
Secondary sex features are characteristics that develop during puberty. Using the process of elimination, options B and D are really primary gender characteristics. Also, option A has more to do with your genetics than your gender.
That leaves option C. Breasts. They are a secondary sex characteristic that develops during puberty.
Hope this helps! :)
