The answer is immune system
The answer i think it changes
Answer:
The main purpose of the circulatory system is to transport blood, oxygen, nutrients and hormones to and from different cells and tissues throughout the body.
Explanation:
This system works hand-in-hand with the respiratory system to facilitate the exchange of oxygen and carbon dioxide within the blood per the alveoli in the lungs.
Cells create tissues which create organs which make up systems so i believe the answer is D i hope this helps :)
1. molecul of DNA 2. dna packed (coild) around histon h1 3.second stage of dna packing -solenoid thread 4. third stage of packing-chromosomal thread 5.chromosome-chromosomal threads are packed inside