Correct option : (c) TtWW could be the genetic makeup of the tall parent. Since half of the progenies are short, the parent plant will also have a set of short genes; all progenies bore violet flowers, which means that violet colour is dominant over white.
According to the law of dominance, a hybridizing between two pure-breeding varieties yields uniforms F1 generation of all dominant offspring. Since here F1 generation consists of short plants with violet flowers and tall plants with violet flowers in an exceedingly 1:1 ratio, the dominant parent isn’t pure-bred. The absence of a dominant allele for flower colour (violet) would make the phenotype of the dominant parent tall with white flowers.
The looks of the recessive trait in the F1 generation (dwarfism) confirms the presence of 1 recessive allele within the dominant parent and makes it heterozygous for plant height (Tt). Since all F1 generation encompasses a violet flower, the dominant parent is homozygous for flower colour. If the dominant parent were double heterozygous (TtWw), the F1 generation would exhibit recessive traits of both plant height and flower colour. But all F1 generation exhibits violet flowers which confirm that the dominant parent is homozygous for flower colour.