What is true about RBCs in humans?

They do not carry $\displaystyle \mathrm{CO}_2$ at all

They carry about $\displaystyle 20$-$\displaystyle 25$ per cent of $\displaystyle \mathrm{CO}_2$

They transport $\displaystyle 99.5$ per cent of $\displaystyle \mathrm{O}_2$

They transport about $\displaystyle 80$ per cent oxygen only and the rest $\displaystyle 20$ per cent of it is transported in dissolved state in blood plasma