What is the end, and the end of the beginning

Winston Churchill Quotes

Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.

Explanation:

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.

the answer to your question is b