Why is the example of DDT included in the unit? O to show that solutions have unintended consequences
to illustrate why pesticides should not be used by farmers
to promote organic farming methods
O to explain the chemical elements of common pesticides

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."

because they are eaten by the frog and the frog getseaten by the snake and the snake by the eagle

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds

these muscles maintain the blood pressure in the vessels. the smooth muscles are innervated by nerves of the autonomic nervous system. when the muscles contract, they cause vasoconstriction of the vessels and increase blood pressure. when the muscles relax, they enable vasodilation of the   blood vessels hence reduce blood pressure.