Unidirectional valves that prevent the blood from flowing backward are found in the

The answer is veins.  These venous valves prevent the backflow of blood  in these vessels. This is because blood in the veins has lower pressure,  because it is flowing back to the heart, and therefore can be overcome by forces such as gravity and pull. The valves are similar in structure to semilunar valves of the heart.  

videntify the dna change shown in the diagram and explain how that change can result in the increased genetic diversity often seen among siblings.identify the dna change shown in the diagram and explain how that change can result in the increased genetic diversity often seen among siblings.

check for the pregnancy rating of drug. if its class c or d see if other alternatives