Answer: The character that falls in love with Helena first is A. Demetrius.
Step-by-step explanation: At the beginning of A Midsummer Night's Dream, Demetrius, a nobleman, is engaged to Helena, the daughter of Nedar. In that way, Demetrius is the first one to fall in love with her; however, throughout the play, he stops loving her and ends up falling in love with Helena's friend, Hermia. When Oberon perceives that Demetrius has rejected Helena, he orders Puck to enchant Demetrius in order for him to love Helena again. However, Puck makes a mistake and enchants Lysander instead. Therefore, Demetrius is the first character that falls in love with Helena. Lysander is the second one.