Which of the following is a source of genetic variation within a species?
a) cloning
b) mutation
c) selection breeding
d) natural selection

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.

the answer would be d

sound moves fastest in solids because the molecules are tightly packed and it allows sound to vibrate