For Those Opposed to Permitting the Self-Selection of More Than

For those opposed to permitting the self-selection of more than one race in the U.S. Census, an important argument is that

A) most people don't really know what race they are.
B) there is no such thing as race, so multiracial makes no sense.
C) identifying as multiracial reduces the strength of numbers of already underrepresented minority groups.
D) younger people are more likely to identify as multiracial than older people.