The detective left no stone unturned to trace the culprit. A. took no pains B. did very irrelevant things C. resorted to illegitimate practices D. used all available means

The correct answer is D. used all available means.

The phrase “left no stone unturned” means to search thoroughly and

carefully for something. In this case, the detective is searching for the culprit of a crime. The detective is using all available means to find the culprit, including interviewing witnesses, searching for evidence, and following up on leads.

Option A is incorrect because the detective is taking pains to find the culprit. Option B is incorrect because the detective is not doing irrelevant things. Option C is incorrect because the detective is not resorting to illegitimate practices.