巡航 中인 배

"the ship is sailing smoothly" Due to many people coming up with these sample sentences sometimes the student should use "the". Other times use "a". With no clear direction from Duolingo regarding which to use when. I suggest "a ship sailing smoothly" should be acceptable. Reported.

Any clue that why there is a "smoothly" in English translation?? I would propose "A cruising ship/boat".