Organized systems of agriculture, the maintenance of herds of domesticated animals, and permanent, year-round settlements marked the. a. Paleolithic Era c. Bronze Age b. Stone Age d. Neolithic Era Please select the best answer from the choices provided A B C D

it takes hundreds of years to become stable.

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blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.