Why Did Congress Abandon Efforts to Enforce Black Voting Rights

Why did Congress abandon efforts to enforce black voting rights and fair elections in the South after 1892?

A) The Supreme Court had ruled that such efforts were unconstitutional.
B) Continued southern resistance persuaded Congress that such efforts were futile.
C) Race riots in several urban cities greatly decreased public support for civil rights action among northern voters.
D) Voters largely rejected Republicans and their policies in 1890,giving control of Congress and the presidency to the Democrats.