Read this and answer the question. If the question is unanswerable, say "unanswerable".

There is a variety of annual events, beginning with the relatively new New Year's Day Parade, fireworks display at the London Eye, the world's second largest street party, the Notting Hill Carnival is held during the late August Bank Holiday each year. Traditional parades include November's Lord Mayor's Show, a centuries-old event celebrating the annual appointment of a new Lord Mayor of the City of London with a procession along the streets of the City, and June's Trooping the Colour, a formal military pageant performed by regiments of the Commonwealth and British armies to celebrate the Queen's Official Birthday.

Every June, the Trooping of the Colour celebrates what event?
the Queen's Official Birthday