The correct answer is D) First stage: gravimetric. Second stage: inclined plate coalescer. Third stage: polishing filter coalescer. This represents the correct sequential order of the three stages in a typical oily-water separator. The gravimetric stage is the first and most basic stage, using gravity to separate out larger oil droplets. The inclined plate coalescer is the second stage, where smaller oil droplets are combined into larger ones through a series of inclined plates. Finally, the polishing filter coalescer is the third stage, which uses a fine filter to remove the remaining small oil droplets. The other answer choices do not represent the proper sequential order of the three stages in a typical oily-water separator system.