Concept:The idiom "a white elephant" refers to something that is expensive to maintain and offers little practical value, i.e., a costly burden.Explanation:The phrase comes from ancient practice where white elephants were considered sacred but cost a fortune to feed and house. Today, it describes an asset that becomes a financial drain rather than a benefit. For instance, a large stadium with high maintenance but low usage is called a white elephant. Among the options, "Costly burden" fits perfectly. "Lucky charm" implies good luck, "valuable item" suggests high worth, and "rare animal" is about scarcity—none capture the sense of a heavy, unwanted expense.Answer:C. Costly burden