Definition: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Input: Question: According to the Frank-Starling mechanism of the heart, under physiological conditions the cardiac output is directly proportional to: 
 Options:  <1> The size of the ventricle. <2> The heart rate <3> The venous return. <4> The thickness of the myocardium. <5> All the previous answers are correct.
