Biological Traits Generally Follow a Geographic Continuum,also Called a Cline

Biological traits generally follow a geographic continuum,also called a cline.How does this relate to the concept of race?

A) Most traits are not bounded by supposed "racial" boundaries but rather vary between two points,such as the frequency of type-B blood changing gradually from eastern Asia to far-western Europe.
B) The cline is the scale against which variation is measured,from which we can derive the number of distinct races in a region.
C) The term clinal variation is another term for race or subspecies.
D) Most genetic traits sort people into a fixed number of race categories.Clines do not sort people this way but are very rare.