Mendel accounted for the observation that traits which had disappeared in the F₁ generation reappeared in the F₂ generation by proposing that

A)new mutations were frequently generated in the F₂ progeny, "reinventing" traits that had been lost in the F₁.
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 obscured by the dominant ones in the F₁.
D)the traits were lost in the F₁ due to dominance of the parental traits.
E)members of the F₁ generation had only one allele for each trait, but members of the F₂ had two alleles for each trait.