People who have migrated from the plains to an area near Rohtang Pass six months ago will exhibit which of the following characteristics?

• A
  They will have more $RBC$s and their hemoglobin will have a lower binding affinity to $O_2$.
• B
  They will not be physically fit to play games like volleyball.
• C
  They will suffer from altitude sickness,such as nausea and fatigue.
• D
  They will have a normal $RBC$ count but their hemoglobin will have a higher binding affinity to $O_2$.