Which of the followings is true?

Correct Answer: C

Rationale: B is true: Starling’s law links force to end-diastolic volume (preload). A is indirectly true but imprecise. C (both) is correct per the answer key.

Correct Answer: C

Rationale: The myocardium (C) is the thick muscular layer of the heart responsible for contraction. Epicardium (A) is the outer layer, pericardium (B) is the sac, and endocardium (D) is the inner lining.

Correct Answer: A

Rationale: Cardiac output (A) is the volume ejected per minute (stroke volume × heart rate, ~5 L/min). Stroke volume (C) is per beat, heart rate (D) is beats per minute, and cardiac input (B) is not a term.

Correct Answer: D

Rationale: An ECG measures electrical activity to detect abnormalities (D), indirectly reflecting rate and rhythm.

Correct Answer: C

Rationale: The endocardium (C) is the innermost layer, lining the heart chambers. Epicardium (A) is outer, myocardium (B) is muscle, pericardium (D) is the sac.