Concept: An idiom is a phrase or expression whose meaning cannot be deduced from the literal meanings of its constituent words. "A white elephant" is a common English idiom.
Step 1: Understanding the idiom "a white elephant" The idiom "a white elephant" refers to a possession that is:
Expensive to maintain or upkeep.
Difficult or troublesome to manage.
Ultimately of little use or value, or its cost and trouble outweigh its benefits.
Often, it's something that is not easy to get rid of. The origin is said to come from the practice of kings of Siam (now Thailand) supposedly giving actual white elephants (which were considered sacred and could not be put to work) as "gifts" to courtiers they disliked. The recipient would be financially ruined by the cost of maintaining the sacred animal.
Step 2: Applying the meaning to the sentence "The luxury car that they bought turned out to be a white elephant." This implies that the luxury car, while perhaps initially desirable, became a burden – possibly expensive to run, maintain, insure, or repair, and perhaps not as useful as expected, making its overall cost and trouble greater than its worth to them.
Step 3: Analyzing the options
(1) a rare article: While a white elephant itself is rare, the idiom doesn't primarily mean rarity. It means something burdensome.
(2) useful mode of transport: This is the opposite of what a white elephant usually implies. If it were useful without being a burden, it wouldn't be a white elephant.
(3) costly or troublesome possession: This perfectly captures the meaning of "a white elephant." It's a possession that costs a lot (either to acquire or maintain) and/or causes a lot of trouble, and may not be worth it.
(4) a proud possession: While one might initially be proud of a luxury car, if it becomes a "white elephant," the pride is likely overshadowed by the burden. The idiom focuses on the negative aspects of the possession.
Step 4: Identifying the best expression of meaning Option (3) "costly or troublesome possession" best expresses the meaning of the idiom "a white elephant." (Note: "trouble some" in the option should ideally be "troublesome").