Which of the Following Statements Correctly Describes How Mendel Accounted

Which of the following statements correctly describes how Mendel accounted for the observation that traits had disappeared in the F₁ generation and then reappeared in the F₂ generation?

A) New mutations were frequently generated in the F₂ progeny, causing traits that had been lost in the F₁ to reappear in the F₂.
B) The mechanism controlling the appearance of traits was different between the F₁ and the F₂ plants.
C) Traits can be dominant or recessive, and the recessive traits were "hidden" by the dominant ones in the F₁.
D) Members of the F₁ generation had only one allele for each trait, but members of the F₂ had two alleles for each trait.