Which sentence contains parallel structure?
a. we are called to honor our own words of reverent people with resolution in the deeds we must perform to preserve peace and the hope of freedom.
b. it is empty to plead that the solution to the dilemmas of the present rests on the hand of the clock. the solution is in our hands.
c. one hundred years ago, the slave was freed. one hundred years later, the negro remains in bondage to the color of his skin.
d. we, the living, have not forgotten-and the world will never forget-the deeds or the words of gettysburg.