The fact that each plant gets only one allele from each parent plant is detailed in the law of

Segregation

Explanation:

The fact that each plant gets only one allele from each parent plant is detailed in the law of law of segregation. Mendel found that each pair of alleles segregates independently of the other pairs of alleles during gamete formation. When sperm and egg unite at fertilization, each contributes its allele, restoring the paired condition in the offspring. The allele pairs separate or segregate during gamete formation, and randomly unite at fertilization.

the correct answer is b