I believe it is B. The meaning of bias is prejudice in favor or against someone or a group compared to another in an unfair way. Many can have a one sided opinion about something such as who is going to win the race. However, choosing different cheese is more of an opinion showing which they prefer more than being bias.
Since inspired air is 21% oxygen and atmospheric pressure is 760 mmHg (at sea level), the partial pressure of oxygen is 0.21 x 760 mmHg = 160 mmHg. As air moves into the alveoli, water vapor and carbon dioxide are added, and that reduces the partial pressure of oxygen to about 100 mmHg in the alveolar gas.