Why are reciprocal crosses variable? Are they?

Reciprocal crosses give different results. This is how Morgan came up with idea of -linkage. Cross a zygous, red-eyed female Drosophila with white-eyed male, knowing that red-eye (wild-type) is dominant, ie, the cross is XRXR x XrY. Then cross a white-eyed female, with a red-eyed male, ie, XrXr x XRY. Notice that the F1s are different; I believe (C) is the best answer...