Which phylum has members that secrete a hard, calcium carbonate shell?
- Arthropoda
- Nematoda
- Cnidaria
- Mollusca

i believe your answer would be Mollusca.

Explanation:

(i looked it up on britannica if you have any questions.) Mollusk, also spelled mollusc, any soft-bodied invertebrate of the phylum Mollusca, usually wholly or partly enclosed in a calcium carbonate shell secreted by a soft mantle covering the body.

significant amounts of nitrogen oxides, carbon monoxide, and other pollution

explanation:

passenger vehicles are a major pollution contributor, producing significant amounts of nitrogen oxides, carbon monoxide, and other pollution. in 2013, transportation contributed more than half of the carbon monoxide and nitrogen oxides, and almost a quarter of the hydrocarbons emitted into our air.