Answer:option C=> Civil Rights Act of 1964
Step-by-step explanation:
The Civil Rights Act that made it illegal for businesses, motels, restaurants, and public transportation providers to deny citizens service based on their race is that of the Civil Rights Act of 1964.
For option A,The Civil Rights Act of 1866 was enacted to define citizenship, the Civil Rights Act of 1866 made sure that all slaves are freed.
For option B, theCivil Rights Act of 1871 was enacted to protect African- American people from violence especially from the Klan.
For option D,Civil Rights Act of 1991 was passed/enacted so as to make Amendments to the Civil Rights Act of 1964.