In a cash journal, what can you not do?

In the context of a cash journal within SAP, the primary characteristic is that it's designed to handle cash transactions in a straightforward manner. One important aspect of this is the limitation on posting transactions in multiple currencies. Cash journals are typically set up for a single currency, which aligns with the principle of efficiently managing cash transactions without the complexity that comes from foreign currency exchange.

This limitation helps streamline the cash handling process, as it focuses on providing clear and concise records tied to one currency. This ensures that cash balances are easily monitored and reduces potential errors that can arise from currency conversions and fluctuations.

The other options address different functionalities of the cash journal, which include being able to manage open items, modify existing entries, and use multiple accounts as needed for accounting purposes. However, the inability to handle multiple currencies is pivotal in maintaining the simplicity and effectiveness of cash management within the cash journal concept.