Which of the following is the most basic oxide?

The correct option is A $B{i}_2{O}_3$
The acidic or basic nature depends upon the oxidation state of the metal present in the oxide.
Out of the all the options, $Se$ is present in the $+4$ state, while the rest three metals are in $+3$
Furthermore, the basic character of the oxides rises with the increasing size of the central atom for a given oxidation state. $Bi$ has a larger size than $Al\text{and}Sb$. Thus, $B{i}_2{O}_3$ is most basic among all.
Therefore, the correct answer is D.