Answer:
AA
Step-by-step explanation:
A true breeding organism for a particular trait is an organism that would produce progeny with the same trait whe self fertilized.
Hence, since axial flower is represented by the allele A, a true breeding flowering plant will have the genotype AA.
Axial flower (A) is dominant over terminal flower (a).
True-breeding axial flowering plant will have the genotype AA.
True breeding terminal flowering plant will have the genotype aa.
AA is crossed with aa.
AA x aa
offspring: Aa, Aa, Aa and Aa.
All the offspring will exhibit axial flowering.