A true-breeding petunia plant with red petals was crossed with another true-breeding petunia plant with white petals. The plants of the F1 progeny had blue petals. When these F1 plants were selfed, the resulting progeny consisted of 243 plants with blue petals, 81 plants with red petals and 108 plants with white petals. 

(A) Which of the following can be reduced from the above data?

a. The formation of blue petals needs activity of two genes.

b. The formation of red petals needs activity of three genes.

c. The formation of white petals needs activity of a single gene.

d. The two true-breeding strains are mutated in the similar locus.