The completion of the Transcontinental Railroad greatly affected companies that made products in that it made it far easier for them to transport their goods over long distances to markets, which greatly increased profits and output.
I could add a fourth category that you could consider in your answer if you are allowed to do that.
Fourth: the leaders of the movement
In point of fact, all of them were effective. The Supreme court heard many cases on the right to vote and the right to be treated as though color were not a determining factor on voting rights. These cases helped bring about the Civil Rights act of 1964 and the Voting rights act of 1965. It put teeth into the 15th amendment, all of which you should look up.
Martin Luther King made a huge impact on Civil Rights. One of key ideas that he had was civil disobedience. Even that was strongly opposed by people like Governor George Wallace. That aside, civil disobedience was a method that peaceful people could tie into and participate in. Look up Rosa Parks as the primary example of someone very welling to stand her ground.
When you look up the Civil Rights act you will see that the Federal Government played a key role in making and enforcing key laws.
The people were ready to determine their rights as citizens. The time was right to unite the participants. Even students themselves were involved in "the people" many of whom were from many parts of the United States. You could google students civil rights movement. People your age were very influential.
