(b) That's probably right, but the answer to this type of question requires some careful distinctions to be drawn. In Australia, it has been held by the Supreme Court of New South Wales that no special duty of care arises towards persons with an individual condition that makes them especially susceptible to harm.
But 'persons with a particular condition' may be a class of persons to which harm is foreseeable in particular circumstances. For example, in Haley v London Electricity Board [1965] AC 778, on which this case-study is closely based, it was held that if it is foreseeable that the persons who are exposed to harm by careless conduct includes persons suffering from conditions such as blindness, then a duty of care will extend to such persons, and sufficient measures must be taken to prevent the harm that might result from their condition. In the present case, A is likely to owe a duty of care to B.