Final answer:
Providing real estate investment advice can be performed without a real estate license, while managing rentals, selling commercial properties, and conducting open houses generally require one.
Step-by-step explanation:
Out of the activities listed, Option 4: Providing real estate investment advice could be performed without a real estate license. This is because providing advice on real estate investment typically falls under financial advising, rather than the activities that require a real estate license, such as selling or managing properties on behalf of others. However, it is important to ensure compliance with any local regulations regarding financial advice.
Options such as managing rental properties for others, selling commercial real estate, and conducting open houses for someone else's property would all generally require a real estate license. These activities involve representing a third party in real estate transactions or managing their property, which necessitates formal authorization and a license to ensure accountability and professional standards.