What scientific breakthrough was made in the 1940s and 1950s? paleontology

natural selection

DNA research

cell theory

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.

is this for the e2020 class

digestion

it excretes wastes

i think its white blood cells

i hope this