The Dub in “lub dub” is the closing of the and valves because pressure in the arteries is greater than in the .

The first heart sound (lub) can be heard the loudest at the mitral area. This sound represents the closure of the mitral and tricuspid valves and is a low pitched, dull sound at the beginning of ventricular systole. S2 – The second heart sound (dub)

b. the carbon cycle ensures living things have a source of hydrogen

the actual answer was 160934