The toxic effect of carbon monoxide is due to its greater affinity for haemoglobin as compared to oxygen by (approx.) (in $times$)

Blood is a medium to transport $O_{2}$ and $CO_{2}$. About ...$A$... per cent of $O_{2}$ is transported by ...$B$... in the blood and the remaining ...$C$... per cent of $O_{2}$ is carried in a dissolved state through the ...$D$...
Select the right options for $A, B, C$ and $D$ to complete the given statement.

Carbon dioxide entering the red blood cells reacts with water to form carbonic acid. Which enzyme is responsible for this reaction?

Carbon dioxide is transported via blood to lungs mostly in which form?

The haemoglobin of a human foetus:

What are the major transport mechanisms for $CO_{2}$? Explain.