Complex sentence: The Downtown Line is the fifth Mass Rapid Transit line in Singapore and opened in three stages, on 22 December 2013,27 December 2015 and 21 October 2017 respectively.
Split into simpler sentences: The Downtown Line will be the fifth Mass Rapid Transit line in Singapore. It opened in three stages, on 22 December 2013,27 December 2015 and 21 October 2017 respectively.