The Hindu Adoptions and Maintenance Act, 1956, lays down several mandatory conditions for a valid adoption.
\[\begin{array}{rl} \bullet & \text{**Section 7** requires that any male Hindu who wishes to adopt must be of **sound mind** and not a minor. (A is correct).} \\ \bullet & \text{**Section 10** states the persons who may be adopted. It requires the child to be a Hindu and not already adopted. Crucially, it also states that the child must not have completed the age of fifteen years (**a minor**), unless there is a custom or usage applicable to the parties which permits adoption of older children. (B is correct).} \\ \bullet & \text{Registration is not a mandatory condition for the validity of the adoption itself, although a registered adoption deed creates a presumption of validity (Section 16).} \\ \end{array}\]
Since both (A) and (B) are essential conditions, (D) is the correct answer.