Queen and Prince Philip walk on stage for ceremony

The video discusses the new Center for Elephant Care, highlighting pregnancy scans and the role of keepers. It introduces baby elephant Elizabeth, born in June 2016, and her growth milestones. The video concludes with the unveiling of a plaque to commemorate the center's opening.

What event was celebrated last year that is mentioned in the text?

What is the purpose of the plaque that was to be unveiled?