The methyltransferase domain of the polymerase subunit 1a in the cucumber mosaic virus is responsible for doing with of the following?

A) Separating strands of the viral RNA during replication.
B) Replicating the viral genome.
C) Adding the 5' cap to the viral RNA genome segments.
D) Movement of the viral genome through the plasmodesmata.
E) Inhibiting host ribonucleases.