Project file is incomplete. Expected imports are missing vs2017

I’m a beginner. I git clone the demo from GitHub - MonoGame/MonoGame.Samples at 3.7, and I open with the vs2017, then output error as the title. I google it, try to fix it by install different .Net Core verson,but it doesn’t work.
OS: window 7
IDE: Visual Studio 2017 Version 15.9.51
Monogame Version: 3.7.1
Demo Version: 3.7