Design an experiment that would help you collect the data you have identified in question four. Identify your independent variable(s), dependent variable(s), treatments, and control

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.