Is it true that you need to have .NET Core 3.1 SDK to build and run cross-platform applications?

The statement that .NET Core 3.1 SDK is required to build and run cross-platform applications is true because .NET Core is fundamentally designed to be a cross-platform framework. It allows developers to create applications that can run on different operating systems, such as Windows, macOS, and Linux, without significant changes to the codebase.

The .NET Core 3.1 SDK includes the necessary tools, libraries, and runtime needed for developing applications that leverage .NET Core capabilities. By having this SDK installed, developers gain access to the command-line tools and APIs necessary to compile and run their applications smoothly across various environments.

On the other hand, the other statements do not accurately reflect the necessity of .NET Core SDK for cross-platform development. For instance, while server applications can require specific SDK versions based on the framework used, general cross-platform development is supported by having the appropriate version of .NET Core SDK installed. The option suggesting it depends on the project does not apply universally since the framework standardization implies that to build and run any cross-platform application, the SDK is essential.