Explanation:

- Option 1: An income

- Subscription received in advance isn't classified as income yet. Income is recognized when the service is rendered, aligning with the accrual accounting principle.

- Option 2: An asset

- This is incorrect. Assets are resources owned by the company, providing future economic benefits. A subscription advance is not this.

- Option 3: A liability

- This is correct! Subscription received in advance is a liability because the company has an obligation to provide services in the future.

- Option 4: None of these

- This is not applicable, as Option 3 already correctly identifies the classification as a liability.