Answer:
The first heart sound (S1) represents closure of the atrioventricular (mitral and tricuspid) valves as the ventricular pressures exceed atrial pressures at the beginning of systole (point a). S1 is normally a single sound because mitral and tricuspid valve closure occurs almost simultaneously.
Explanation:
Dna is my bun. Sisnsisnddidncidndjdid
Enzymes lower the activation energy level of a chemical reaction, thus enabling the reaction to proceed. Hope this helps
Carbon dioxide, sunlight, and water