A person who agrees to serve as mediator between two warring factions at the request of both abandons by so agreeing the right to take sides later. To take sides at a later point would be to suggest that the earlier presumptive impartiality was a sham.
The passage above emphasizes which of the following points about mediators
(A) They should try to form no opinions of their own about any issue that is related to the dispute.
(B) They should not agree to serve unless they are committed to maintaining a stance of impartiality.
(C) They should not agree to serve unless they are equally acceptable to all parties to a dispute.
(D) They should feel free to take sides in the dispute right from the start， provided that they make their biases publicly known.
(E) They should reserve the right to abandon their impartiality so as not to be open to the charge of having been deceitful.
By pointing out the consequences of abandoning impartiality， the paragraph points out the importance for mediators of maintaining impartiality at all times. This is the point made in Choice B， which is therefore the correct answer. Choice A is incorrect， because it goes further than anything asserted in the passage. The passage does not rule out the possibility that one can have an opinion about issues related to a dispute without taking sides in the actual dispute. Choice C is incorrect because it is a presupposition on which the passage is based rather than the point of the passage; that is， the fact that the mediator is acceptable to both parties is a given， since they both ask the mediator to serve. Choices D and E are both inconsistent with the main point of the passage， the importance of impartiality at all times， so both are incorrect.