Why Is Biological Race Difficult to Determine

Why is biological race difficult to determine?

A) Measurement reveals that people are as different from others classified in the same race as they are from those in different races.
B) We do not know how many skeletal traits ultimately constitute a different race.
C) Most people cannot see beyond their prejudices and do not consider the appropriate traits in their classification.
D) Internal traits are more important in the separation of races than those which we see superficially.
E) Race does not exist biologically or socially.