Which of the following operating arrangements allows an FCC-licensed US citizen to operate in many European countries, and amateurs from many European countries to operate in the US?

The European Conference of Postal and Telecommunications Administrations (CEPT) establishes multilateral agreements that simplify amateur radio operations across international borders. For US citizens holding a valid FCC license, the CEPT agreement allows them to operate in many European countries without needing to apply for a temporary license from the host country. Similarly, this reciprocal arrangement allows amateurs from participating European nations to operate their radios while visiting the United States. You simply operate using your home call sign with the appropriate prefix for the country you are visiting, as defined by the agreement. The IARP (International Amateur Radio Permit) is a different arrangement that primarily applies to participating countries in the Americas, not Europe. ITU reciprocal licenses do not exist as a singular blanket agreement in the way CEPT does.