Air pollution in us and canadian cities is caused mostly by a. clear-cutting forests for timber b. releasing emissions from vehicles and industry c. dumping runoff from farms into rivers d. harvesting minerals from mines

Most air pollution in United States and Canadian cities is caused by vehicle and industrial emissions. The correct option among all the options that are given in the question is the fourth option or option "D". This has led to increased amount of global warming. I hope the answer has helped you.

these conditions long with a short growing season made farming difficult.

explanation:

the north has a climate of warm summers and snowy cold winters. the terrain is rocky, hilly, and not good for farming.

d: social contract theory