Under which circumstances must contracting officers solicit sealed bids?

The correct choice emphasizes that contracting officers must solicit sealed bids primarily when time allows, and the decision for awarding the contract is based exclusively on price. This aligns with federal procurement regulations, which define sealed bidding as a method used when offers are evaluated based on price alone, ensuring a fair and transparent process. Sealed bids are typically used for straightforward procurements where price is the determining factor, utilizing a competitive process to secure the best price for the government.

In contrast, the other options do not fully encapsulate the requirements for sealed bids. While it may be beneficial to expect multiple bids or consider the nature of the products being acquired, these factors alone do not necessitate the use of sealed bidding. Additionally, while products exceeding the micro-purchase threshold indicate a need for a more formal process, this alone does not specifically require sealed bids unless other criteria, such as price competition, are met. Hence, the focus on price and the allowance of time for bid solicitation is key to understanding when sealed bidding is appropriate.