If pure tall and pure dwarf pea plants are crossed, which trait usually appears in the first generation?

Correct answer: All plants tall

Let pure tallness be TT and pure dwarfness be tt. Each F1 offspring receives T from the tall parent and t from the dwarf parent, so every offspring has genotype Tt. Because T is dominant over t in this Mendelian example, all F1 plants show the tall phenotype. Thus option A is correct; dwarf plants would be expected after a suitable later-generation cross, not in this F1 cross.