Carbon monoxide (CO) is toxic to humans because it:
A. is rapidly converted to toxic CO2.
B. binds to myoglobin and causes it to denature.
C. binds to the globin portion of hemoglobin and prevents the binding of O2.
D. binds to the heme portion of hemoglobin and causes heme to unbind from hemoglobin.
E. binds to the Fe in hemoglobin and prevents the binding of O2.