Concept:The letter "C" in the folio column of a cash book indicates a contra entry.
Explanation:When a transaction involves both the cash column and the bank column of the same cash book, it is called a contra entry.
For example, cash deposited into the bank or cash withdrawn from the bank for office use.
In such a case, the letter "C" is written in the folio column.
This shows that both aspects of the double entry are already recorded within the cash book itself.
Therefore, no further posting to the ledger is necessary for that transaction.
Answer:C. contra entry