(b) That's probably wrong. The plaintiff must be a person or a member of the class of persons who it was foreseeable might suffer harm as a result of the defendant's conduct. The extent to which different classes of persons might foreseeably be harmed by particular conduct can be quite wide. One such class of persons would be A's friends or other persons invited by A onto his property. Another class of persons who would foreseeably be harmed by A's conduct would be persons making deliveries to his property, or meter readers. It is also foreseeable that uninvited persons such as unsupervised children or other trespassers might enter A's property and suffer harm. And persons who do not actually enter A's property might suffer harm indirectly: for example, B's parents.
In some circumstances, harm is caused to a person who belongs to a class or group of persons who it could not reasonably be foreseen would be harmed by the defendant's conduct. In such cases there would be no duty of care owed to that plaintiff. In this example, D is likely to be such a person.