When Does Death Occur from Carbon Monoxide Poisoning

When does death occur from carbon monoxide poisoning?

A) When all the hemoglobin molecules in the blood complexes with CO.
B) When about one fourth of the hemoglobin molecules in the blood complexes with CO.
C) When about three fourths of the hemoglobin molecules in the blood complexes with CO.
D) When about ten percent of the hemoglobin molecules in the blood complexes with CO.
E) When about half the hemoglobin molecules in the blood complexes with CO.