Blood flow from lungs to left atrium

Steps:

• Nicotine enters blood via alveoli in lungs and joins oxygenated blood.
• This blood travels through pulmonary veins toward the heart.
• Pulmonary veins empty directly into the left atrium.
• Left atrium is the first heart chamber to receive this blood.

Why A is correct:

• The left atrium receives oxygenated blood from pulmonary veins, per standard pulmonary circulation anatomy.

Why the others are wrong:

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

Final answer: A