Why does the expected genotypic ration often differ from the expected phenotypic ratio resulting from monohybrid cross

The genotypic ratio and phenotypic ratio are different when a monohybrid cross is done because multiple genotypes often result in the same phenotype.

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.