How did the great depression of the 1930s help the blues to spread?
选项：

A:.Many people from the south, including blues musicians, travelled north to the big cities.
B:.Many people from the north, including blues musicians, travelled south to the big cities.
C:.Many people from the west, including blues musicians, travelled east to the big cities.
D:.Many people from the east, including blues musicians, travelled west to the big cities.