Final answer:
Two heterozygous black mice are expected to produce offspring in a 3:1 phenotypic ratio of black to white. Option A, with three black and two white offspring, is the only option that fits the expected outcome of such a cross. Therefore, the correct option is a.
Step-by-step explanation:
The question concerns a genetic cross between two heterozygous black mice, and which is a possible litter outcome from such a cross. When two heterozygous individuals (Bb) are crossed, the typical outcome is a 3:1 phenotypic ratio according to Mendelian genetics. This means that approximately 75% of the offspring are expected to exhibit the dominant phenotype (black in this case), and about 25% are expected to exhibit the recessive phenotype (white). Therefore, any litter that follows this ratio is possible. Option A (Three black offspring and two white offspring) fits the expected ratio, while the other options do not match the expected results of a Mendelian cross. So, the correct answer is: A. Three black offspring and two white offspring.