What is it called when landforms are slowly worn down over time by outside forces?

Weathering. Weathering happens when forces in nature break down rocks into smaller pieces. Think of the tiny grains of sand on a beach. Those grains of sand used to be parts of larger rocks or shells. Over time, pieces of the larger rocks or shells broke off.

Explanation:

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.

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