The correct answer is Pure line
The parents in a monohybrid cross they are pure line.
Monohybrid cross is termed as mating which is between two organisms whereby their variations are different to one genetic interest of chromosomes.
In order to carry out a monohybrid cross the parent should be homozygous.
Relationship dominance which is between two alleles is being determined by monohybrid cross.
One allele is for homozygous for one parent and the other parent is homozygous for the other allele.