Mutations are changes to an organism's DNA and are an important driver of diversity in populations. Species evolve because of the accumulation of mutations that occur over time. The appearance of new mutations is the most common way to introduce novel genotypic and phenotypic variance. Some mutations are unfavorable or harmful and are eliminated from the population by natural selection. Others, which are beneficial, spread through the population. Some mutations have no effect on an organism and can linger, unaffected by natural selection, in the genome while others can have a dramatic effect on a gene and the resulting phenotype. Some mutations, which are harmful do not get eliminated from the gene pool because they are recessive and carried by heterozygous individuals. Thus, option B is correct.