Complex sentence: The knockout stage of the 2007--08 UEFA Champions League began on 19 February 2008, and concluded on 21 May 2008 with the final at the Luzhniki Stadium, Moscow.
Split into simpler sentences: The knockout stage of the 2007--08 UEFA Champions League began on 19 February 2008. It is set to be completed on 21 May 2008 with the final at the Luzhniki Stadium, Moscow.