Although both humans and nature cause this corrosive precipitation, approximately what proportion of acid rain is attributable to humans? a.) 1/4b.) 1/2c.) 2/3d.) 3/4

2/3 proportion of acid rain is attributable to humans.

Explanation:

Acid rain occurs due to the presence of nitrogen oxides and sulphur dioxides in atmosphere, which on reacting with water produces sulphuric and nitric acids. The automobiles, burning of fossil fuels, industrial smoke, coal-burning are all man-made and contribute the release of sulphur dioxides and nitrogen oxides in the atmosphere causing acid rain.

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.

the truman doctrine was an american foreign policy whose stated purpose was to counter soviet geopolitical expansion during the cold war. it was announced to congress by president harry s. truman on march 12, 1947, and further developed on july 12, 1948, when he pledged to contain threats to greece and turkey.