Question

red blood cells appear red because:
a of the size of their nucleus.
b they contain hemoglobin.
c they contain bilirubin.
d they transport oxygen.

Explanation:

Hemoglobin in red - blood cells binds to oxygen and has a red - orange color, giving red blood cells their red appearance. The size of the nucleus has no relation to their color. Bilirubin is related to the breakdown of red blood cells and is not the reason for their red color. Transporting oxygen is a function, not the cause of their color.

Answer:

B. they contain hemoglobin.