The “separate but equal” doctrine established by the supreme court in plessy v. ferguson (1896) upheld the legality of
(1)woman’s suffrage in state elections
(2)the activities of the ku klux klan
(3)racial segregation in public facilities
(4)restrictions on voting rights of african americans

Racial segregation in public facilities

Explanation:

In public sites, rooms and services were separated for whites and blacks. They claimed to be 'separate but equal'. The Plessy vs. Ferguson case upheld this doctrine by supporting its legality.

So, the answer is (3) racial segregation in public facilities.

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