Which of the following statements about Carbon Monoxide poisoning is not true:

• A. Partial pressures as low as 0.6 mm Hg can be lethal
• B. Carboxy haemoglobin (COHb) causes left shift of oxyhaemoglobin dissociation curve
• C. Hyperbaric oxygen is used for treatment
• D. Tissue toxicity plays an important role in clinical CO poisoning