Can you plzzz help me?!! and hurry plz? it's biology

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Secondary pollutants are more harmful than primary pollutants. select the best answer from the choices provided ot of

What is hydroelectric power produced by?

What would be the result if crossing over did not happen during meiosis in humans? a. there would be less genetic variation in humans. b. parents would be more likely to look like their children. c. the human population could not reproduce. d. children would have more chromosomes.