How Was the "Grandfather Clause" Used to Keep African Americans

How was the "grandfather clause" used to keep African Americans from voting in the South?

A) It was a device that allowed whites who had failed the literacy test to vote anyway by extending the franchise to anyone whose ancestors had voted prior to 1867.
B) It was a tax that had to be paid as a condition of voting and was prohibitively expensive for most African Americans in the South.
C) It was a primary election that was open only to whites.
D) It was a primary election that was only open to those African Americans who could prove that their grandfathers had lived in the same district.
E) It was a device that only allowed those African Americans to vote whose grandfathers were still alive.