How can the dwarf trait reappear in the second generation even if it is not visible in the first generation?

Correct answer: Because it remains hidden as a recessive form in the first generation

In the F1 generation from a pure tall TT × pure dwarf tt cross, all plants are Tt. The dominant T allele masks the recessive t allele, so dwarfness is not expressed, but the t allele remains present. When F1 plants self-pollinate, the F2 combinations include TT, Tt, Tt, and tt. The tt plants express dwarfness, so option A is correct.