Do selected tests in Text Explorer window in Visual Studio 2015 run concurrently or sequentially?

In Visual Studio 2015 for C#,

1. if I select several tests in the Test Explorer window, and right click to choose run the selected tests, will the selected tests be run simultaneously, or sequentially (i.e. one test starts automatically when the previous test finishes)?

2. How can I specify to run the selected tests sequentially, or concurrently?

3. If the tests are run simultaneously, is synchronization between different tests necessary?

Thanks.