The correct options are
A Due to the unity of various ethnic groups
B Due to the unity of various cultures
C Due to the unity of various races
The South Africans call themselves a rainbow nation due to the unity of various cultural, racial, or ethnic groups seen in the country in the post-apartheid era. "Rainbow Nation" is a term coined by Archbishop Desmond Tutu to describe post-apartheid South Africa, after South Africa's first fully democratic election in 1994.