This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Which of the following is seen in high altitude climbersa) Hyperventilationb)  Decreased PaCO2c)  Pulmonary edemad)  Hypertensione) Bradycardia 
Select and explain. 
A. ab, B. abc, C. acd, D. bcd
B: abc
Answer: B: abc 
Explanation: At high altitude, there can be acute changes and changes due to acclimatization.
-  Acute mountain sickness

Dyspnoea, dizziness, tiredness, tachycardia, palpitation, nausea, vomiting etc.
At higher altitudes- pulmonary oedema and cerebral oedema may occur.

- Acclimatization changes

Hyperventilation leading to respiratory alkalosis
Increased 2,3DPG- Hb-O2 dissociation curve shifts to right.
Increased erythropoietin leading to absolute polycythemia with increased red cell mass.
Increased renal excretion of bicarbonate
Increased tissue vascularity
Increased oxidative metabolism
Increased diffusion capacity of the lung​
Increased myoglobin