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

The correct answer is A. discerning.

Perspicacious means having or showing keen insight and discernment. It is a synonym for astute, sharp-witted, and intelligent. In the context of the question, the judicial investigation officer was able to quickly find the cause of the problem because they were discerning. They were able to see things that others could not see, and they were able

The other options are incorrect. Mysterious means difficult or impossible to understand. Clever means having or showing quick mental ability and resourcefulness. Quick means moving or happening quickly.