The correct answer is: A. Who is feeding the child?
The other options are incorrect because they do not refer to the current state of the child being fed. Option B, Who has fed the child?, refers to a past event, while option C, Who was feeding the child?, refers to an event that was happening at a specific time in the past. Option D, Who has been feeding the child?, refers to an event that has been happening repeatedly over time.
The question “By whom is the child being fed?” asks who is currently feeding the child. The answer to this question could be a person, such as a parent or caregiver, or it could be an animal, such as a mother cat feeding her kittens.