The chromatogram produced from a chromatography test on substance S is displayed. Distances shown on the chromatogram are $4.5\ \text{cm}$, $4.7\ \text{cm}$, $6.0\ \text{cm}$ and $1.8\ \text{cm}$, and the solvent front and baseline are marked. What is the $R_f$ value of S?
- A0.39
- B0.46
- C0.56
- D0.62