Which of the following is NOT one of Microsoft Azure's relational database options?

Azure Data Lake is indeed the correct choice as it is NOT one of Microsoft Azure's relational database options. Azure Data Lake is primarily designed for big data analytics and storage, providing a scalable and secure data lake solution for large amounts of structured and unstructured data. Its purpose is to enable data scientists and analysts to work with vast datasets and perform analytics, rather than serving as a traditional relational database service.

On the other hand, SQL Server in a VM, SQL Managed Instance, and Azure SQL Database are all relational database services provided by Azure. They are designed to manage structured data through the use of tables, relationships, and strict schemas, thus meeting the requirements of relational database systems. SQL Server in a VM allows users to run SQL Server on virtual machines, SQL Managed Instance provides a fully managed instance option, and Azure SQL Database offers a fully managed, scalable cloud database service. Each of these options is built to handle relational data efficiently.