Veins have a much lower blood pressure than arteries. which of these prevents backflow of blood in veins?
a. pressure applied by the heart
b. one–way valves in veins
c. thin muscular walls of veins

Which of these best describes what occurs during cytokinesis? a) the chromosomes are separated b) the cell begins to divide by replicating the chromosomes c) the cytoplasm is divided between the two new daughter cells d) the nucleus opens to allow the chromosomes to enter the cytoplasm

Approximately what portion of the foods that we eat have been genetically modified in some way? a.fewer than 10% b.about 50% c.nearly 100%

How much time has elapsed from the very beginning of "the memior of the conquistador bernal diaz del castillo" to the end? a. castillo's whole life b. a quarter of an hour c. a few weeks d. a decade