People who have migrated from the plains to an area adjoining Rohtang Pass about six months back:

• A
  have more $RBCs$ and their haemoglobin has a lower binding affinity to $O_2$
• B
  are not physically fit to play games like football
• C
  suffer from altitude sickness with symptoms like nausea,fatigue,etc.
• D
  have the usual $RBC$ count but their haemoglobin has very high binding affinity to $O_2$