Which of the following defects is most likely to be found in yeast cells with a dramatically increased rate of genomic mutation per cell cycle?

A) Activation of a G1/S DNA damage checkpoint in the absence of DNA damage.
B) Activation of a G1 restriction point checkpoint despite adequate cell size and nutrient supply.
C) A nonsense mutation within a DNA replication polymerase.
D) An inactivating mutation within a gene encoding an essential component of the unreplicated DNA checkpoint.
E) Activation of a G2/M DNA damage checkpoint in the absence of DNA damage.