Concept:The war or quarrel between Lysander and Demetrius is caused by Helena.Explanation:In Act III, Scene Two, both Lysander and Demetrius have been struck by the love potion.They now abandon Hermia and both fall in love with Helena.Each man challenges the other to a duel, hoping to prove whose love for Helena is greater.Therefore, Helena is the immediate reason for the bitter conflict between the two men.Answer:Helena (Option A).