Given the task definition and input, reply with output. This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

In 1977, Elizabeth marked the Silver Jubilee of her accession. Parties and events took place throughout the Commonwealth, many coinciding with her associated national and Commonwealth tours. The celebrations re-affirmed the Queen's popularity, despite virtually coincident negative press coverage of Princess Margaret's separation from her husband. In 1978, the Queen endured a state visit to the United Kingdom by Romania's communist dictator, Nicolae Ceaușescu, and his wife, Elena, though privately she thought they had "blood on their hands". The following year brought two blows: one was the unmasking of Anthony Blunt, former Surveyor of the Queen's Pictures, as a communist spy; the other was the assassination of her relative and in-law Lord Mountbatten by the Provisional Irish Republican Army.
What Jubilee did Elizabeth celebrate in 1977?