In Furman v. Georgia, the Supreme Court ruled that the death penalty violated the Eighth Amendment because the death penalty was A
used to deter criminals
B
used in nonviolent cases
C
applied unequally across states.
D
already abolished in most states

C. applied unequally across states.

Explanation:

The case of Furman V. Georgia occured in 1972. At that time, most states did not necessarily 'Banned' the use of death penalty as a punishment. But the problems occurred because it seems that each states have different standard when determining which type of criminals should be sentenced with death penalty.

Example of the unequal application :

Furman was sentenced to death penalty because he killed someone during an attempted robbery.  But criminals who convicted with the same charge in California at that time was punished with 25 years of prison time. Not death penalty.