Which is a recommended response type to respond to either a threat or an opportunity?

Fallback is a threat-only response that involves preparing a contingency plan to be enacted if the threat materializes; it has no applicability to opportunities.

Reject is an opportunity-only response, used when the organization decides not to exploit a potential positive risk; it does not apply to threats.

The 'Share' response involves using a third party to share the risk or benefit - for a threat, this means partnering to share the potential negative impact (similar to transfer), and for an opportunity, it means sharing the positive outcome with a partner. Because it can be directed at either a downside or an upside event, it is classified as a dual-purpose response in the PRINCE2 risk management framework.

Reduce is a threat-only response aimed at lowering the probability or impact of a negative risk event; it is not a valid response to an opportunity.