It was very perspicacious of the judicial investigation officer to find the cause of the problem so quickly.

Answer: Option A

Discerning : having or showing good judgement.
Mysterious : difficult or impossible to understand, explain, or identify.
Clever : quick to understand, learn, and devise or apply ideas; intelligent.
Quick : moving fast or doing something in a short time.
Perspicacious : having a ready insight into and understanding of things.

Synonym of Perspicacious is Discerning