"The train station, the ferris wheel"
Translation:Nhà ga, đu quay
Used as a classifier, cái means the for inanimate objects. For animate objects (subjects?) you must use another classifier, i. e. con or người.
Among the most common classifiers are:
cái: used for most inanimate objects
chiếc: almost similar to cái, usually more connotative (e.g. when referring to a cute object, chiếc might be more suitable than cái)
con: usually for animals and children, but can be used to describe some non-living objects that are associated with motion like a river, a knife, a street/road, etc.
người: used for people except infants
bài: used for compositions like songs, drawings, poems, essays, etc.
câu: sentential constructs (verses, lyrics, statements, quotes, etc.)
cây: used for stick-like objects (plants, guns, canes, etc.)
chuyện: a general topic, matter, or business
lá: smaller sheets of paper (letters, playing cards)
tòa: buildings of authority: courts, halls, "ivory towers"
quả/trái: used for globular objects (the Earth, fruits, eggs)
quyển/cuốn: used for book-like objects (books, journals, etc.)
tờ: sheets and other thin objects made of paper (newspapers, papers, calendars, etc.)
việc: an event or an ongoing process
pity an expert hasn't answered. To aid understanding as it has so many short, similar words, vietnamese has a lot of classifiers: for people it's pronouns, for objects they are classified as animals or inanimate objects, or plants, or vehicles, (or lots of other classes I don't know about!) hence con, cái, etc. For meat, it's 'thịt'. So you can refer to a chicken (con gà) or chicken meat (thịt gà). Classifiers provide contextual understanding and are important. It's just a quirk of the language.
I don't even use the word ferris wheel in my own language, let alone Vietnamese. I don't need to know it. I need to know more important words like bicycle wheel, or steering wheel. These sounds are not difficult in Vietnamese. If you want to teach "đu" then maybe talk about the children on the swing, and for "quay" talk about a car turning left. Maybe those words are wrong but that's what Google suggests. Please choose something more appropriate to learn.