Read the statement: When Mendel crossed a purple-flowered pea plant with a white-flowered pea plant, the offspring always had purple flowers. When Mendel crossed the offspring with each other, the second-generation offspring had some white-flowered plants.
What conclusion can be drawn from this observation?

A. There is a chance that any second-generation plant will be a white-flowered one.
B. White-flowered plants showed up every other generation in pea plants.
C. The first-generation plants would also have white-flowered ones. Mendel did not do enough trials.
D. The genes of pea plants somehow changed in their second generation.