The Final Step in a DNA Sequencing Reaction Is to Run

The final step in a DNA sequencing reaction is to run the DNA fragments on a gel.What purpose does this serve?

A) It adds ddNTP to the end of each DNA fragment.
B) It changes the length of the DNA fragments.
C) It separates DNA fragments based on their charge.
D) It separates DNA fragments generated during the sequencing reaction based on one-nucleotide differences in their size.