Answer:
Explanation:
Organisms have different forms of circulatory systems. Humans have a closed circulatory system, while many mollusks and other invertebrates have an open system. In a closed circulatory system, blood is enclosed within blood vessels.
Explanation:
it is the diagram of an ovum or a human egg
A- follicle cells
B- zona pellucida
C- chromosomes
D- vitelline membrane
I'm not 100% sure, but I'd say the availability of vaccines and medicine.