The correct option A-3, B-1, C-4, D-2 aligns with specific UN peacekeeping operations in relation to their respective periods of operation. UNMIL (United Nations Mission in Liberia) was active from 2003-2018, aimed at maintaining peace post-civil war, hence matched with 3. MINURCAT (United Nations Mission in the Central African Republic and Chad) operated from 2007-2010, correlating with 1. MINUSTAH (United Nations Stabilization Mission in Haiti) functioned from 2004-2017, which coordinates with 4. Lastly, UNMISET (United Nations Mission of Support in East Timor) was active from 2002-2005, matching it with 2. Understanding these operations is crucial for grasping the UN's role in global peacekeeping efforts and the geopolitical contexts of each mission, significant themes in UPSC GS Paper I.