**Explanation:**

The correct answer is option C - "A credit balance in the ledger will be either a revenue or a liability."

To understand why this is the correct answer, let's break down the different options and their meanings:

**a) A revenue or an asset:**
- Revenue is the income generated from the primary activities of a business, such as sales of goods or services.
- Assets are resources owned by a business that have economic value and can be used to generate future benefits.
- While a credit balance in the ledger could represent revenue, it does not necessarily indicate an asset. A credit balance could also indicate a liability.

**b) An expense or an asset:**
- Expenses are costs incurred in the process of generating revenue. They decrease the overall profit of a business.
- Similar to option a, a credit balance in the ledger could represent an expense, but it does not necessarily indicate an asset.

**c) A revenue or a liability:**
- As mentioned earlier, revenue represents the income generated from the primary activities of a business.
- A liability, on the other hand, is an obligation or debt owed by a business to external parties.
- A credit balance in the ledger could represent revenue earned but not yet received (i.e., revenue yet to be collected from customers). In this case, it is considered a liability because the business has an obligation to collect the revenue from customers.
- Alternatively, a credit balance could also represent an overpayment or advance received from a customer. In this case, it is also considered a liability because the business has an obligation to provide goods or services in the future to the customer to offset the overpayment.

**d) An expense or a liability:**
- As discussed earlier, expenses represent costs incurred in generating revenue.
- Liabilities are obligations or debts owed by a business to external parties.
- While an expense could be represented by a credit balance in the ledger, it does not necessarily indicate a liability.

Based on the above explanations, option C - "A credit balance in the ledger will be either a revenue or a liability" is the correct answer.