Answer: TT, Tt
Step-by-step explanation:
it could only be one of 3 things homozygous dominate (TT) Homozygous Recessive (tt) or heterozygous (Tt)
with only 3 possible combinations it makes it easy to see what ones would be Tall
Think about it like this
If it has a dominate allele (T) it will always be tall
It needs 2 Recessive Alleles (tt) to be short