B

The postwar economic development did not last long.When the Great Depression began in 1929，Canada was severely affected.Drops in wheat prices on international market ruined many farmers in the west，and dry weather turned parts of the prairies into a“dust bowl”.Agricultural income fell by as much as 75％ and wheat production in 1937 was only one⁃third that of 1928.Industry was hit hard too because of the fall in purchasing power caused by the Depression.Gross national product fell by 40％between 1929 and 1932，and in 1933，32％ of the national labor force was unemployed.

Although the Liberal Government was replaced by the Conservative Party in 1930，the economy did not improve and many people suffered greatly.When World War Ⅱ began in 1939，Canada still had 400，000 people unemployed.