Oxygenated blood in the left heart chambers

Steps:

• Recall that deoxygenated blood enters the right atrium (likely part 1) from the body.
• It moves to the right ventricle (likely part 2) and pumps to the lungs for oxygenation.
• Oxygenated blood returns to the left atrium (likely part 3) from the lungs.
• It flows to the left ventricle (likely part 4) and pumps to the body.

Why D is correct:

• Oxygenated blood fills the left atrium and ventricle after pulmonary circulation, per the heart's double-circuit system.

Why the others are wrong:

• A includes right-side chambers with deoxygenated blood.
• B mixes right ventricle (deoxygenated) with left atrium (oxygenated).
• C mixes right ventricle (deoxygenated) with left ventricle (oxygenated).

Final answer: D