In 1990 and 1991, apartheid and all the laws that supported it were

abolished

Explanation:

South Africa was a country where for pretty long time there was racial segregation on pretty much every level. This segregation came to be known as apartheid.

Basically, the white South Africans were controlling everything in the country. They were running all the businesses, thus having full control of the economy, had all the institutions at disposal, every opportunity in life available int he country, controlled the wealth, controlled the politics etc.

In meantime, the black South Africans were not allowed to educate themselves, didn't had political or economic influence, the opportunities for jobs were very limited, and they were not allowed to live or visit places were the white South Africans lived or were using.

This all changed in 1990 and 1991, when the apartheid was abolished. This came as a result from the revolt by the black population, international pressure, and threat of economic sanctions toward South Africa.

Instead of improving the situation in the country, it actually just seems that the things were reversed, as nowadays it is the black population that terrorizes the white population without any sanction for it, and the reason being revenge and expelling the white population out of South Africa.

a and b because with the other three, they simplify to something else.