What functions do schemas perform – are they necessary? this is about the biology of memory.

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.

it has one origin of replication, but it proceeds in two directions - d)