If an X Determines Femaleness and a Y Determines Maleness

If an X determines femaleness and a Y determines maleness, why doesn't gender testing necessarily determine the gender of an athlete?

A) It's difficult to find the X and Y chromosomes in a human karyotype.
B) Not everyone gets an X and/or a Y chromosome.
C) A sexual development disorder can make a person with a Y still essentially female.
D) A sexual development disorder can make a person with two Y's still essentially female.
E) Estrogen from the mother can overwhelm the instructions from the Y chromosome, resulting in a female.