The correct answer is A. Casual.
Sage is a word that means wise or having experience and knowledge. A sagacious decision is a wise or well-considered decision. Casual means not serious or not done with care. Cunning means clever or crafty in a way that is intended to deceive. Foolish means lacking good sense or judgment. False means not true or correct.
In the sentence “It was a sagacious decision on his part,” the word “sagacious” is used to describe the decision. The decision is described as being wise or well-considered. This means that the decision was made after careful thought and consideration. The decision was not made casually or without care. It was also not made in a clever or crafty way that was intended to deceive. The decision was made in a way that was based on good sense and judgment.
The other options are incorrect because they do not accurately describe the decision. The decision was not casual, cunning, foolish, or false.