At which locations are staff exempted from liquid restrictions?

The correct choice highlights that staff are exempted from liquid restrictions at Irish state and regional airports that are secured by Ryanair. This exemption exists primarily due to the controlled security environment at these airports, which allows for specific relaxation of certain standard procedures typically applied to passengers.

In general, liquid restrictions are in place at most airports to enhance security and prevent the transportation of dangerous liquids on board aircraft. However, staff working at secured airports often undergo comprehensive security training and background checks, thus allowing them to carry necessary items for their roles, including liquids that are otherwise restricted for regular passengers.

The other options involve varying airport types and jurisdictions, where general rules about liquid restrictions would apply. International airports outside the EU, all airports in the EU, and private airports often adhere to stricter liquid policies due to security regulations that aim to mitigate risks associated with liquid explosives in passenger baggage. Therefore, the exemption is specifically nuanced for staff working at Ryanair's secured facilities in Ireland.