请教一个Verbal题

banboshuyingUID: 2905157

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.
麻烦帮我分析一下，谢谢！

无敌浩克OneUID: 3605802

就是Mediator他不能选择支持任何一方，开始时不能，之后也不能