diff --git a/InterfaceStudy.Core/IBase.cs b/InterfaceStudy.Core/IBase.cs
index 6a332f4..5d3a7f2 100644
--- a/InterfaceStudy.Core/IBase.cs
+++ b/InterfaceStudy.Core/IBase.cs
@@ -12,6 +12,6 @@ namespace InterfaceStudy.Core
     /// </summary>
     public interface IBase
     {
-         int GetNumber();
+        int GetNumber() { return 1; }
     }
 }
diff --git a/InterfaceStudy.Core/InterfaceStudy.Core.csproj b/InterfaceStudy.Core/InterfaceStudy.Core.csproj
index 9f5c4f4..f45bdfc 100644
--- a/InterfaceStudy.Core/InterfaceStudy.Core.csproj
+++ b/InterfaceStudy.Core/InterfaceStudy.Core.csproj
@@ -1,7 +1,7 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFramework>netstandard2.1</TargetFramework>
   </PropertyGroup>
 
 </Project>