Which of the following statements about chromatography is accurate?
- AIt is not possible for two different substances to have the same $R_f$ value.
- BIt is only possible to use chromatography on substances which have a colour.
- CIt is possible to use chromatography on colourless substances using a locating agent.
- DThe $R_f$ value of a substance = $\frac{\text{the distance travelled by the solvent}}{\text{the distance travelled by the substance}}$