Witch source should be avoided when conducting scientific research

When performing scientific research, one must always avoid using personal biases so that there are no errors or interruptions. Hope this helps you.

personal biases so that there are no errors or interruptions

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.