Which of the following is a reason for the rapid manufacturing and commercial expansion experienced ...

Which of the following is a reason for the rapid manufacturing and commercial expansion experienced by the Northeast during the forty years following the War of 1812?
 
  a. The unparalleled natural increase in the population of the North and South increased demand formanufactured products.
 b. The federal government poured vast sums of money into the building of factories and the building of canals.
  c. Transportation costs were dramatically reduced as a result of extensive internal improvements.
  d. After the war most European nations refused to import goods to the United States, thus domesticmanufacturing expanded rapidly in the Northeast to meet consumer demand.