Which Statement Comparing Human Adult and Fetal Hemoglobin Is True

Which statement comparing human adult and fetal hemoglobin is true?

A) Fetal hemoglobin contains one particular subunit that lowers its P₅₀.
B) Fetal hemoglobin contains one particular subunit that raises its P₅₀.
C) All subunits of fetal hemoglobin are different and result in a lower P₅₀.
D) All subunits of fetal hemoglobin are different and result in a higher P₅₀.