African Americans who moved north

A. usually returned to the South within three years.

B. were looking for economic opportunity.

C. avoided working in so-called sick industries.

D. were safe from violence and discrimination.

B

Explanation:

They went to the North in order to avoid violence, discrimination and slavery; and also look for jobs. Basically they wanted a better life. They weren't technically safe from violence and discrimination, it was still there - but they wanted to avoid it.

B. African Americans migrated north for Economic opportunity to support their families