The correct answer here is A and E.
The main function of the introductory word in sentence 2 would be that "<span>It is a transition word," since it helps show the time in which this event is taking place (at the same time, that is). </span>
Balance of power is talking about the legislative, judicial, and executive branch which were all made to keep each other "balanced out" where they can check other branches and make sure that decisions being made aren't "unconstitutional" so that there wouldn't be one person with total power that could lead to a dictatorship.
