The correct answer is: B. Authorisation of transactions.
Vouching is the process of verifying the authenticity of a transaction by examining the supporting documentation. This documentation can include invoices, purchase orders, receipts, and other evidence that the transaction took place. The objective of vouching is to ensure that the transaction was authorized and that the goods or services were received.
Option A is incorrect because vouching does require knowledge of the entire business transaction. The auditor must understand the nature of the transaction, the parties involved, and the terms of the agreement.
Option C is incorrect because vouching does not require knowledge of the transactions unrelated to business. The auditor is only concerned with the transactions that are relevant to the audit.
Option D is incorrect because only option B is correct.