Red blood cells can contain a molecule called 2,3-bisphosphoglycerate (2,3-BPG). If 2,3-BPG binds to haemoglobin, a greater partial pressure of oxygen is required to achieve $50\%$ saturation of haemoglobin with oxygen. Which statements concerning the effect of 2,3-BPG are correct?
- A1 and 2
- B1 and 3
- C2 and 3
- D3 and 4