Answer:
Hybrid Tall Plants.
Step-by-step explanation:
The thing is for this the tall trait is dominant meaning that if someone has one individual dominant allele, it will bring out the tall phenotype. Now, the short trait is recessive, this essentially just means that certain someone needs to have two copies of the recessive allele to bring out the short phenotype, it's polar opposites essentially.
In this specific case, the purebred tall plant contains 2 copies of the dominant allele (TT) and the purebred short plant has 2 copies of the recessive allele (tt). So when the 2 plants are crossed, the resulting offspring will get 1 copy of the dominant allele from the tall parent and 1 copy of the recessive allele from the short parent. Furthermore, the genotype out of all this would be Tt (making this a hybrid tall trait!!!).
The thing is though... since the dominant allele is expressed in the phenotype, the offspring will be:
Tall.