Concept:The sales day book is the book of original entry for all credit sales made to customers.
Explanation:Every credit sale is recorded in the sales day book with details such as the customer's name, invoice number, date, and amount.
At the end of the period, the total of the sales day book gives the total credit sales for that period.
The cash book records only cash receipts and cash payments, not credit sales.
The petty cash book is used for small cash expenses, not sales transactions.
Returns inwards records goods that customers returned, which reduce sales rather than show credit sales.
Therefore, the correct source for total credit sales is the sales day book.
Answer:B. sales day book