Answer:
Option B, the principle of segregation
Explanation:
While conducting experiment on the pea plants, Gregor Mendel in 1865 found that some newly produced pea plant were not exactly the same as that of their parents. This made Mendel conclude that the allele pair on the chromosome that represents certain traits get separated during cell division and he termed this process as principle of segregation.
In this question, Marcus genotype Bb need to split in order to give "B" allele to one sperm and "b" allele to another sperm thereby setting an example of "principle of segregation"