Hello! You did not list which genotype was dominant, but I will do my best anyway:
When you cross the genotypes TT and tt for the two plants, it is only possible to get the genotype Tt.
No matter what, the answer is NOT A OR D!
If the short genotype is dominant, the answer is C.
If the tall genotype is dominant, the answer is B (Tt crossed with Tt in a punnet square produces one tt)
I hoped this helped you! Without the dominant trait being listed it was harder to answer but I did my best :)