a)Tallness is the dominant trait.
A cross between a tall plant (TT) and short pea plant (tt) resulted in progeny that were all tall plants because tallness is the dominant trait. In F1 generation, the cross between TT and tt will result in all tall plants. Thus, tallness is the dominant trait. Whenever two traits of a character are crossed, the F 1 plants show only one of the traits, this trait is called as the dominant trait. The other trait (dwarfness) that does not express itself in F1 generation is called as the recessive trait.