The reapers are aware of the Lady of Shalott's presence on the island because - a. they have seen her through a window b. they have seen her wandering the island c. they hear her singing d. Lancelot tells them about her

They are aware of the Lady of Shalott's presence on the island because C. they hear her singing.

They know there is a woman there in the tower, however, they can't really see her. They can only hear her sing her sad song. She is unable to leave her island because of the curse cast on her, however, when she spots an attractive knight, she falls in love with him, leaves her tower, and dies because of the curse.

They hear her singing