We can rewrite the passage as:
The five persons were involved in a series of scandals(fraud convictions and mismanagement); a sixth person (responsible for the daily operation) would curb corruption.We have to look for an answer that shows us, for example, that the 6th member will not be able to control the others, or will not have power on the others, or something similar.
A. The council manager, though a voting member of the council, would not be allowed to introduce new legislation.
Does the scandals invole "new legislations"? No, so this limit of the 6th person's powers will not affect his effectiveness.
B. The council manager would have no control over other board members’ decisions about funds disbursement.
IMO CORRECT: These frauds will not be limited by the 6th person, so his effectiveness is limited.
C. Each council member represents over 15,000 constituents and would not have time to talk with all of them.
This is not a good point to say that he cannot curb the corruption.(refer at the top)
D. The council manager is required to have a background in either accounting or business administration.
This is not a good point to say that he cannot curb the corruption.
E. The city council must cooperate with the county government, which is also made up of elected officials.
This is out of scope.
Waiting for the OA