The correct answer is option B. Higher levels of haemoglobin
A higher level of the haemoglobin allows the organism to survive in low oxygen condition. The low oxygen level decreases the amount of oxygen delivered to the cells, to cope up this condition, there is an increase in the haemoglobin content. The increased haemoglobin concentration allows the delivery of the sufficient amount of oxygen, as the number of haemoglobin increase, the capacity of oxygen carried to the cell is increased.