Which of the following methods of improving air quality does not require advanced technology?

a. exhaust scrubbing

b. conservation

c. using renewable energy sources

d. driving fuel-efficient cars

Conservation is the one method of improving air quality among the following choices given in the question that does not require advanced technology. The correct option among all the options that are given in the question is the second option or option "b". This method only needs preserving the natural balance.