Q: 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.
On October 17, 1987, about 3,000 Armenians demonstrated in Yerevan complaining about the condition of Lake Sevan, the Nairit chemicals plant, and the Metsamor Nuclear Power Plant, and air pollution in Yerevan. Police tried to prevent the protest but took no action to stop it once the march was underway. The demonstration was led by Armenian writers such as Silva Kaputikian, Zori Balayan, and Maro Margarian and leaders from the National Survival organization. The march originated at the Opera Plaza after speakers, mainly intellectuals, addressed the crowd.
A:
When was the Yerevan demonstration?