Since the other answer got deleted, i'll just answer it for you.
a sinoatrial node is the main pacemaker that begins each heartbeat located in the junctions of superior vena cava and the right atrium. It signals from the node that spread through the atria and determines the heart rates.
The correct answer is D(<span>Neck, armpit, and groin). I took the test and know from personal experience.
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Answer:
C. Nucleus
Explanation:
In both animal and plant cells the nucleus controls all activities in the cell.
Answer:
Arteries have thick walls composed of three distinct layers (tunica) Veins have thin walls but typically have wider lumen (lumen size may vary depending on specific artery or vein) Capillaries are very small and will not be easily detected under the same magnification as arteries and veins.
Explanation:
DNA and Histones Form bread-like globules known as nucleotides
