Q.Cash book is a :

The cash book is both a subsidiary book and a principal (ledger) book, so the answer is (c).

The cash book has a dual nature:

• As a subsidiary book (book of original entry), all cash and bank transactions are first recorded in it directly from source documents, just like purchases and sales books. …

A simple cash book doubles as the Cash account, so a separate Cash account need not be kept in the ledger — option (c).

Why:

• A simple (single-column) cash book records all cash receipts on its debit side and all cash payments on its credit side.
• It is a book of both original entry and ledger at the same time — its balance is exactly what a Cash account in the ledger would show. …