Prairie dogs are an example of

a. an abiotic factor
b. a producer
c. a keystone species

Prairie dogs are keystone species. Over 160 native birds and animals depend for food and shelter upon the rich ecosystem prairie dogs create, like ocean fish depend on coral reefs. Prairie dog colonies are the coral reefs of the sea of grass

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.