The 13th, 14th, and 15th amendments to the constitution were undermined by all of the following except a) jim crow laws. b) literacy tests. c) plessy v. ferguson. d) brown v. board of education.

D)Brown v. Board of Education.

Explanation:

Brown v. Board of Education (1954) struck down the "separate but equal" doctrine established in Plessy v. Ferguson. Segregation of white and black children in the public schools of a State solely on the basis of race, denies to black children the equal protection of the laws guaranteed by the Fourteenth Amendment.

answer: the time zones used to be whatever the local authority wanted them to be. one town might have 6am whenever the sun came up and another town had 6am 10 minutes later.  

the trains had a hard time when their orders said to be at a certain point at 6am.  

6am, but who's 6am.  

the railroads got together and set the time zones more or less along the longitude lines across the country.

explanation: