A student investigates some food colourings, each of which is made up of one or more dyes.
She produces a chromatogram using the safe colourings red (SR), blue (SB) and green (SG)
and food colourings red (FR), blue (FB) and green (FG).
The diagram shows her chromatogram.
How many dyes are there in SR?
A 1 B 2 C 3 D 4