I received a pm for the explanation of question
Mayor Drabble pg-4 of this thread.
It would be very easy to get 2 contenders for this questions viz a and e. Rest of the options are as bad as they can be.
Now lets keep in mind the argument and try to personalize the argument for better understanding.
An example how to personalize an argument(You may have a different way,depends upon person to person)
Let me keep myself in place of Mayor Drabble :
So, we know that I owe Lee a fairly recent political debt, and Lee wants to be appointed to head the arts commission. Since i always repay my political debts “as soon as possible,” I will repay all the previous debts I can before fulfilling my obligation to Lee. So if we want to conclude that Lee will get the appointment he wants, we have to assume that no one else who would like to head the arts commission is ahead of Lee in the line for political repayment by me.
E stands as a close contender. Lets see what's wrong with E:
The OE says :
It’s not absolutely necessary to assume that Lee’s debt can only be repaid in one way. And even if the author does make this assumption, it doesn’t complete the argument. The author still need to assume that the mayor won’t first repay one of her older debts by
appointing someone besides Lee to head the arts commission
A better way to kick out E is Personalize.
Lets say the only way to repay MY political debt(remember I am Mayor D

) is to appoint is to appoint Lee as head. But what if Mr. Shawn is also one of the contender whom I owe a political debt of longer standing than Lee. Certainly Lee won't become the Head then. So this leaves the argument vulnerable to criticism and an assumption is something which safeguards the argument. So definitely, this is not the assumption.
I am so sorry that I skipped the explanation for this question.Some Difficult questions like this one require in-depth analysis and I appreciate your feed back.