(D) is the right answer.
The term multigene families is used to include groups of genes from the same organism that encode proteins with similar sequences either over their full lengths or limited to a specific domain. DNA duplications can generate gene pairs. If both copies are maintained in subsequent generations then a multigene family will exist. A multigene family is a member of a family of related proteins encoded by a set of similar genes. Multigene families are believed to have arisen by duplication and variation of a single ancestral gene. Examples of multigene families include those that encode the actins, hemoglobins, immunoglobulins, tubulins, interferons, histones etc. DNA duplications that involve one or more genes generate gene pairs. If both copies are maintained in subsequent generations then a multigene family will exist in the genome. Because most duplications occur adjacent to the original copy, a subsequent duplication encompassing both paralogs may generate a family of four. Chromosomal rearrangements disperse the multigene families throughout the genome. Dispersed members of the multigene family can still be recognized by sequence comparison.