The answer is:
C. Puck dropped love juice from a flower in Lysander's eyes while he slept.
In Shakespeare's "A Midsummer Night's Dream," Oberon, king of the fairies, tells Puck to put the juice from a flower on Demetrius' eyes so that he will wake up and fall in love with the first woman he sees. Even though he commands Puck to make sure the first person Demetrius sees is Helena, Puck makes a mistake and gives the potion to Lysander. As a result, Lysander sees Helena first and falls in love with her, so he no longer loves Hermia.
