Which parts of the heart prevent backflow of blood in the circulatory system and allow the heart to work like a pump? a.)atria b.)valves c.)ventricles

Compare the depth of field when focusing with low power and high power. which power has the greater depth of field?

Spring tides, when the high tides are at their highest and low tides at their lowest. what is it about these positions that causes these high and low tides?

Of your good in bio kusing a series of preliminary observations; pstate a problem developed from these observations, formulate a hypothesis, design an experiment to test the hypothesis