Multiple choice

The blood vascular system of mammals is known as double vascular system, because

  1. a group of veins carry oxygenated blood and other group conduct deoxygenated blood

  2. oxygenated blood runs from heart to different organs by one set of vessels, while deoxygenated blood runs from heart to lung by another set

  3. the two different systems never meet

  4. all of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Mammals have a double circulatory system: pulmonary circulation (heart to lungs and back) carries deoxygenated blood, while systemic circulation (heart to body tissues and back) carries oxygenated blood. The two circuits are separate and don't mix. Option A is incomplete, C is wrong (circuits connect at the heart chambers).

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