A cross between two tall pea plants resulted in offsprings having a few dwarf plants. The gene-combination of the parental plants must be

For dwarf plants (which have the homozygous recessive genotype $tt$) to appear in the offspring of two tall plants, each parent must contribute one recessive allele ($t$). Since both parents are tall, they must also possess at least one dominant allele ($T$). Therefore, both parental plants must be heterozygous tall, with the gene combination $Tt$ and $Tt$.

• Option B (Tt and tt): A cross between $Tt$ (tall) and $tt$ (dwarf) would indeed produce dwarf plants, but the question states that the cross is between two tall pea plants. Since $tt$ is dwarf, this option is incorrect.
• Option C (TT and tt): This is a cross between a homozygous tall and a dwarf plant, which violates the condition that both parents are tall. Also, all offspring of this cross would be tall ($Tt$).
• Option D (TT and Tt): A cross between $TT$ (homozygous tall) and $Tt$ (heterozygous tall) will only produce tall offspring ($TT$ and $Tt$). No dwarf plants ($tt$) can be produced because the $TT$ parent can only pass on the dominant allele $T$.