Blood flow from lungs to left atrium

Steps:

• Nicotine enters blood via alveoli in lungs.
• Blood in lungs flows into pulmonary veins.
• Pulmonary veins deliver oxygenated blood directly to left atrium.
• Left atrium is first heart chamber encountered.

Why A is correct:

• Pulmonary veins carry blood from lungs to left atrium, per standard pulmonary circulation pathway.

Why the others are wrong:

• B: Left ventricle receives blood after left atrium contracts.
• C: Right atrium receives deoxygenated blood from systemic veins, not lungs.
• D: Right ventricle receives blood from right atrium and pumps to lungs.

Final answer: A