Which of the following can be considered a type of auction?

A sealed-bid auction is a type of auction where bidders submit their offers without knowing the other participants' bids. This format encourages participants to make strategic decisions based on their valuations of the item, as they must consider how much to offer without any direct competition insight. The auction concludes with the highest bid winning the item, and this allows for a transparent and competitive environment while safeguarding bidders' confidentiality regarding their offers.

In contrast, a fixed-price sale and a regular sale do not have the competitive bid aspect inherent to auctions. A fixed-price sale sets a definitive price that does not fluctuate based on bidder interest, while a regular sale may encompass a variety of transactional methods but typically does not involve the structured competition characteristic of auctions. Similarly, a trade-in auction refers to a scenario involving trade-ins and is not recognized as a formal type of auction in the same sense as sealed-bid or open-outcry auction formats.