In summer squash, white fruit (W) is dominant over yellow fruit (w) and the "disk" fruit shape (D) is dominant over "sphere" shape (d). Determine the genotypes of the parents in the following cases:
A. White disk crossed with yellow sphere gives 1/2 white disk and 1/2 white sphere.
B. White sphere crossed with white sphere gives 3/4 white disk and 1/4 yellow sphere.
C. White disk crossed with white disk gives 28 white disk, 9 white sphere, 10 yellow disk plants and 1 yellow sphere plant.