The correct option is A Miracidium
Miracidium larva is an elongated, free-swimming stage. It is covered with flat ciliated epidermal cells lying in five rings. The miracidium does not feed, it swims in water or moisture film, but it dies in eight hours unless it can reach a suitable intermediate host. After getting a suitable host the miracidium adheres to it by its apical papilla and enters the pulmonary sac of the snail, from where it penetrates into the body tissues with the aid of penetration glands and finally reaches to snail’s digestive gland.