Question

the supreme court decision cited in the text declared that
supreme court of the united states (163 u.s. 537), may 18, 1896
may 18, 1896
—plessy v. ferguson, supreme court of the united states (163 u.s. 537),
the fourteenth amendment...\
\we think the enforced separation of the races, as applied to the internal commerce of the state, neither abridges the privileges or immunities of
the colored man, deprives him of his property without due process of law, nor denies him the equal protection of the laws within the meaning of
this is connected with the establishment of separate schools for white and colored children, which has been held to be a valid exercise of the
legislative power even by courts of states where the political rights of the colored race have been longest and most earnestly enforced.
universally, recognized as within the competency of the state legislatures in the exercise of their police power. the most common instance of
the races are liable to be brought into contact do not necessarily imply the inferiority of either race to the other, and have been generally, if not
universally, recognized as within the competency of the state legislatures in the exercise of their police power. the most common instance of
this is connected with the establishment of separate schools for white and colored children, which has been held to be a valid exercise of the
legislative power even by courts of states where the political rights of the colored race have been longest and most earnestly enforced.
\we think the enforced separation of the races, as applied to the internal commerce of the state, neither abridges the privileges or immunities of
the colored man, deprives him of his property without due process of law, nor denies him the equal protection of the laws within the meaning of
the fourteenth amendment...\
—plessy v. ferguson, supreme court of the united states (163 u.s. 537),
may 18, 1896
supreme court of the united states (163 u.s. 537), may 18, 1896
the supreme court decision cited in the text declared that

minorities could not be denied equal rights.
racial segregation was not unconstitutional.
schools could only educate african americans separately.
rules to keep african americans from voting were not constitutional.

Explanation:

The case of Plessy v. Ferguson (1896) is known for the Supreme Court's decision that established the "separate but equal" doctrine. This doctrine held that racial segregation laws did not violate the Fourteenth Amendment as long as the facilities were equal in quality. So the decision declared that racial segregation (in the context of the laws and facilities discussed, like separate schools for different races) was not unconstitutional. The other options: the first option is incorrect as the decision didn't focus on denying equal rights to minorities in a general "could not be denied" sense (it allowed segregation which was unequal in practice); the second option is too narrow (the decision wasn't just about schools, and the "separate but equal" allowed separate education but the key was the constitutionality of segregation, not just school separation); the fourth option is incorrect as the case wasn't about voting rules for African Americans.

Answer:

the option "racial segregation was not unconstitutional" (the third option from the top).