Can you beat this one?

The student wants to report the result and mark a limit on applying it to ships. Which choice most effectively uses relevant information from the notes to accomplish this goal?

1. AThe laboratory kept coated and uncoated steel plates in saltwater tanks for 30 days.
2. BCoated steel plates lost an average of 0.4 percent of their mass in saltwater, against 2.1 percent for uncoated plates, so the coating will protect the hulls of ships.
3. CMoving seawater may act on the coating differently from the still water in the test tanks.
4. DIn still saltwater, coated plates lost 0.4 percent of their mass against 2.1 percent for uncoated plates, but moving seawater may act on the coating differently.