The father advised his errant son not to maunder about but do something worthwhile.

The correct answer is A.

Maunder means to talk or wander aimlessly. In this context, the father is telling his son to stop wasting time and do something productive.

B. Wander means to walk aimlessly. This is similar to maunder, but it does not have the negative connotation of being unproductive.

C. Run means to move quickly on foot. This is not what the father is telling his son to do.

D. Play means to engage in an activity for enjoyment. This is also not what the father is telling his son to do.