Which of the following pairs of accounts could not appear in the same adjusting entry?
a. Interest income and Interest expense; b salaries payable and salaries expense; c rent expense and prepaid rent; d service revenue and unearned revenue

Have you made an attempt to answer this yourself?

Have you made an attempt to answer this yourself?

Yes, I have. I have read the book, search for examples on the internet and I am confused because I know that assets such as supplies and prepaid accounts when used up become expenses. Unearned revenue is a liability account which has received money for services the company has not performed. As the services are performed the value of unearned revenue decreases but I am not sure what account would off set unearned revenue.

Everything you just said is correct. You've also answered your own question without realizing it. You said "As the services are performed...." Well, where do services performed go?