What is the leading cause of water pollution in the united states?
a. point source pollution
b. nonpoint source pollution
c. lack of regulation
d. none of the above

The correct answer is option B

The leading cause of water pollution in the United States is non point source. The non point source of water pollution can be pollutants coming from different sources.

These sources can be from agricultural sources( pesticides an fertilizers) industrial waste( liquid wastes from the industries of various types) Domestic wastes, et cetera.

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.