This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.

Passage: Since the early 1990s, Estonia is involved in active trilateral Baltic states co-operation with Latvia and Lithuania, and Nordic-Baltic co-operation with the Nordic countries. The Baltic Council is the joint forum of the interparliamentary Baltic Assembly (BA) and the intergovernmental Baltic Council of Ministers (BCM). Nordic-Baltic Eight (NB-8) is the joint co-operation of the governments of Denmark, Estonia, Finland, Iceland, Latvia, Lithuania, Norway and Sweden. Nordic-Baltic Six (NB-6), comprising Nordic-Baltic countries that are European Union member states, is a framework for meetings on EU related issues. Parliamentary co-operation between the Baltic Assembly and Nordic Council began in 1989. Annual summits take place, and in addition meetings are organised on all possible levels: speakers, presidiums, commissions, and individual members. The Nordic Council of Ministers has an office in Tallinn with a subsidiary in Tartu and information points in Narva, Valga and Parnu. Joint Nordic-Baltic projects include the education programme Nordplus and mobility programmes for business and industry and for public administration. Question: What year did Parliamentary co-operation between the Baltic Assembly and Nordic Council start?
1989