Step 1: Understanding the Concept:
A rightward shift of the oxygen-hemoglobin curve means hemoglobin holds onto oxygen less tightly at a given oxygen tension, releasing more of it to the tissues, and the question wants to know which factors drive this shift.
Step 2: Key Formula or Approach:
Check each factor against the Bohr effect, which describes how acidity and carbon dioxide levels change hemoglobin's oxygen affinity.
Step 3: Detailed Explanation:
Lower \( PO_{2} \) describes a position along the curve, the amount of oxygen present, not a change in the curve's shape or hemoglobin's affinity, so it does not cause the shift by itself.
Higher \( H^{+} \), meaning lower pH, stabilizes the low-affinity deoxygenated form of hemoglobin and pushes the curve right; this is the classic Bohr effect.
Higher \( pCO_{2} \) does the same thing through two routes: it binds hemoglobin directly and it generates more \( H^{+} \) through carbonic acid formation, so it shifts the curve right as well.
Because actively respiring tissue produces both more \( H^{+} \) and more \( CO_{2} \) at the same time, these two factors act together, so both cause the shift, and neither one alone captures the full picture.
Step 4: Final Answer:
Both higher \( H^{+} \) and higher \( pCO_{2} \) cause the rightward shift, so the answer is "both (b) and (c)".