Consider a Cell in Which One of the Proteins or Enzymes

Consider a cell in which one of the proteins or enzymes involved in DNA replication is altered in a way that results in an increased rate of single-base changes in the newly synthesized DNA strand. Which function of which protein is MOST likely disrupted in this situation?

A) the unwinding function of helicase
B) the winding stress relief function of topoisomerase II
C) the fragment joining function of DNA ligase
D) the proofreading function of DNA polymerase
E) the strand separation function of single-stranded binding protein