You are teaching a class to OEC candidates and explain that a pre-existing illness may be complicated by the effects of high altitude. In teaching this concept to your class, you explain that the reason for this effect is that:

a. the increased barometric pressure at high altitude makes the heart work harder.
b. less oxygen is available to vital organs at high altitude.
c. dehydration can limit circulating blood volume.
d. nausea makes it difficult for people to take their medications.

Answer: b