7. For radio reception, diffraction is . a. helpful
b. a hindrance
c. cannot tell its effect
d. not a factor

well, i think the correct answer is

B_ a hindrance

poor water quality affects most estuarine organisms, including commercially important fish and shellfish. the pollutants that have the greatest impact on the health of estuaries include toxic substances like chemicals and heavy metals, nutrient pollution (or eutrophication), and pathogens such as bacteria or viruses.

it's unlikely a majority of a large population would agree on issues

hope this : )