The various spaces in the figure in the figure may be labelled as shown.

• The spaces P, Q and R have to be shaded by three different colours definitely (since each of these three spaces lies adjacent to the other two).
• Now in order that no two adjacent spaces be shaded by the same colour, the spaces T, U and S must be shaded with the colours of the spaces P, Q and R respectively.
• Also the spaces X,V and W must be shaded with the colours of the spaces R,P and Q respectively.

Thus, minimum three colours are required.

Hence option D is correct