An accountant of a firm makes a correction entry for an error in a single transaction in which 20.000 TL has been collected but no revenue has been earned yet as follows: CORRECTION ENTRY => debit cash by 15.000 TL, credit unearned revenue by 10.000 TL, credit sales revenue by 5.000 TL. What was the error?

a- The firm has debited cash and unearned revenue by 5.000 TL each and credited sales revenue by 10.000 TL.

b- The firm has debited sales revenue by 5.000 TL and credited unearned revenue by 5.000 TL

c- The firm has debited unearned revenue by 10.000 TL and credited cash and sales revenue by 5.000 TL each.

d- The firm has debited cash and sales revenue by 5.000 TL each and credited unearned revenue by 10.000 TL.

e- Other: