Which one of the following cannot be explained on the basis of Mendel’s law of dominance?

In a monohybrid cross of plants with red and white flowered plants, Mendel got only red flowered plants. On self-pollinating these $F_1$ plants got both red and white flowered plants in $3:1$ ratio. Explain the basis of using $RR$ and $rr$  symbols to represent the geno type of plants of parental generation.

$A$ : Test cross is the tool for knowing linkage between genes.
$R$ : Monohybrid test cross gives two phenotypes and two genotypes.

A pair of contrasting characters is termed as

Explain the Law of Dominance using a monohybrid cross.