Scientists use a process called gel electrophoresis to separate DNA fragments. The process involves placing a mixture of DNA fragments at one end of a slab of porous gel. Then a power source is used to generate an electric potential across the gel. The diagram shows the process of gel electrophoresis. First, DNA fragments, mixed with a restriction enzyme, are placed at one end of a slab of gel. Then a power source is applied; the longer DNA fragments stay near the negatively charged end, and the shorter fragments move toward the positive end.

Gel electrophoresis is successful because of which property of the DNA fragments?

A. The DNA fragments may be positively-charged, negatively-charged, or neutral.
B. The DNA fragments travel at different speeds through the gel.
C. The DNA fragments travel at the same speed through the gel.
D. The DNA fragments chemically react with the gel in different ways.