Its very likely you were told specifically what to do in class, or in the laboratory rules handout, or a sign posted in your lab. The best answer is likely C, but its not an absolute everywhere that the solution wouldn't be disposed of in a solvent can that's been designated "Lab Waste." Your institution's drain system may be very old, or faulty in some other way, or they may want to get you in the habit of not disposing lab waste down the train. This time it may be perfectly all right to dispose of neutralized acid-base titration waste, but what about the ammonia-acetic acid titration, that will be slightly smelly, even if nearly perfectly neutralized. What about a barium sulfate precipitation, barium is as toxic as arsenic.