Which of the following is both a subsidiary book and a ledger?

The correct answer is the "cash book". A cash book is both a subsidiary book and a ledger. It is a subsidiary book because it records all cash transactions for a particular period, including receipts and payments. It is also a ledger because it maintains individual accounts for each cash account, such as the bank account, petty cash account, and cash on hand account. The cash book serves as the primary source of information for the cash and bank balances in the balance sheet and is used to reconcile the bank statement at the end of the month.