Before trying the official release of Visual Studio 2017, I installed Visual Studio 2017 RC and found that my existing Git repository was not recognized. Although I made sure that the Source Control plugin is installed on Git, as shown in the following figure.

Then, I thought, maybe it's just because of the RC edition. Anyway, the official version of Visual Studio 2017 is released today, and I installed it again. I see the same problem. Has anyone encountered the same problem? What is the solution to this problem? I do not think that I need to install the Git Extension separately, since Visual Studio already has a pre-installed extension.