For your first question, the most significant consequence of the European partitioning and mandate system of Southwest Asia after WWI is:
A. The mandate system caused conflict in Southwest Asia because it grouped people together with vast ethnic and cultural differences.
This response accurately reflects the historical outcomes associated with the mandate system, as it often placed diverse and sometimes conflicting groups within artificially drawn borders, leading to ongoing tensions and conflicts.
For your second question, the correct response is:
B. World War I
The Mandate System was established after WWI, during the Treaty of Sèvres and the subsequent League of Nations mandates.