The correct answer is C) Florida.
By 1876, the Southern state that was still controlled by Republicans was Florida.
In the elections of 1876, the Democratic candidate Samuel J. Tilden was winning in the popular votes by 260,000 and only needed one more electoral vote to win the election; he already had 184. But three states were already in dispute: Florida, Louisiana, and South Carolina. Eventually, the US Congress created the Electoral Commission and resolved the situation in March 1877. The victory belonged to the Republican candidate Rutherford B. Hayes. And the Republicans also kept the state of Florida.