When I ____ 18, I celebrate my birthday in the UK. (планы)

The sentence is incomplete and requires input in the dropdown fields. The first dropdown likely expects a condition related to reaching the age of 18, such as 'turn' or 'am'. The second dropdown, preceding 'celebrate my birthday', might be for specifying the manner of celebration or a related detail. Without further context or options for the dropdowns, a definitive answer cannot be provided.