Which observation led Mendel to the idea that traits were controlled by more than a single factor?

Question

A: Crossing two white-flowered pea plants always resulted in a white-flowered pea plant.
B: A trait that was not seen in the first generation was completely gone and never reappeared.
C: Crossing two purple-flowered pea plants always resulted in a purple-flowered pea plant.
D: A trait that was not seen in the first generation may later reappear in the second generation.
is it A?

Answer 1

disagree

Answer 2

is it d