Choose the Correct Answer from the List Below

Choose the correct answer from the list below. Not all of the answers will be used.
-____________: The organic portion of the heme group in hemoglobin.

A) cooperative
B) oxygen
C) fMRI
D) carbamate
E) histidine
F) hyperbolic
G) myoglobin
H) bicarbonate ion
I) sickle-cell anemia
J) protoporphyrin
K) fetal
L) carbonic acid