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

Fallback is a response type that applies only to threats - it involves preparing a contingency plan to be enacted if the threat materializes, and has no equivalent application to opportunities.

Reject is a response that applies only to opportunities - it means consciously deciding not to exploit an opportunity, and is not a valid response type for a threat.

The 'Share' response involves involving a third party to share either the downside of a threat (for example, through a joint venture or insurance-like arrangement) or the upside of an opportunity. Because it is listed in PRINCE2 as a valid response for both threat and opportunity categories, it is the recommended response type that applies to either risk event type. This dual applicability is a key exam distinction.

Reduce is a response that applies only to threats - it aims to reduce either the probability or the impact of a risk event occurring, and is not applicable as a response to an opportunity.