Explanation:

- Opportunities: These are positive external factors that a firm can exploit to its advantage. They provide potential for growth, such as emerging markets or technological advancements. Opportunities help a company expand its market presence or product offerings.

- Warning: This is not a standard term used in strategic analysis. It might imply a prompt or alert about potential issues, but doesn't specifically relate to external factors hindering a firm.

- Threats: These are negative and unfavorable external factors that could create obstacles for a firm. They include competition, regulatory changes, or economic downturns that might harm the business.

- None of these: This option implies that none of the given choices are correct, which isn't applicable here as "Threats" correctly describes the negative external factors.