Directions: In the following question, a sentence is given with four words marked as (A), (B), (C), and (D). These words may or may not be placed in the correct order. Four options with different arrangements of these words have been provided. Mark the option with the correct arrangement as the answer. If no rearrangement is required, mark option (5) as your answer.

Doctors could not culprit(A) the specific toxin(B) that was making the patient sick(C), so they ordered more tests to look for the identify(D).