Answer:
A. Circulatory system
Explanation:
Circulatory system consist of heart,blood cells&blood vessels
Resource? Idk what this question is
Chromosomes are the slender threads that carry genes
Answer:
An atom is composed of two regions: the nucleus, which is in the center of the atom and contains protons and neutrons, and the outer region of the atom, which holds its electrons in orbit around the nucleus.
Explanation: