Answer:
D
Explanation:
He bred two true-breeding strains initially. That means the alleles were homozygous for each gene.
Let's use Tt to represent the height allele: T means tall, t means short; the dominant allele gets the capital letter.
Let's use Pp to represent the flower color allele: P means purple, p means white.
A pure-breeding tall, purple plant would be TTPP.
A pure-breeding short, white plant would be ttpp.
So the cross is D. TTPP x ttpp.
