From the given sentence, the expression that should be changed in order to correct the sentence is, "the robbery of case". The answer is option C. The correct expression should be "the case of robbery" or "robbery case". The word "robbery" is a specific form of case. So the correct sentence should be, "The police say there is no hope to find the stolen painting as far as the case of robbery was reported too late, and too much time was wasted."
