In which scenario would you use Azure Cognitive Services?

Using Azure Cognitive Services is most appropriate when you aim to leverage cognitive capabilities. These services provide a suite of pre-built APIs that allow developers to integrate intelligence into applications without needing extensive machine learning expertise. They enable functionalities such as speech recognition, language understanding, image analysis, and decision-making processes, which can enhance user experience and create more interactive applications.

The other options do not align with the purpose of Azure Cognitive Services. Creating virtual machines involves using Azure's infrastructure services rather than cognitive capabilities. Developing applications may involve various Azure resources, but it doesn't specifically highlight the use of Azure Cognitive Services, which emphasizes cognitive functions. Similarly, data storage solutions are handled by Azure's various storage services, not by services focused on cognitive processes. Therefore, option C distinctly encapsulates the primary use case for Azure Cognitive Services.