diff --git a/WebApi/Entities/QuestionEntity.cs b/WebApi/Entities/QuestionEntity.cs
new file mode 100644
index 0000000..38605d0
--- /dev/null
+++ b/WebApi/Entities/QuestionEntity.cs
@@ -0,0 +1,21 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations.Schema;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Entities
+{
+    public class QuestionEntity
+    {
+        public int Id { get; set; }
+        public string Content { get; set; }
+        public int difficuty { get; set; }
+        public int NbFalls { get; set; }
+        public int IdChapter { get; set; }
+
+        [ForeignKey(nameof(AnswerEntity))]
+        public int IdAnswerGood { get; set; }
+    }
+}
diff --git a/WebApi/ExtensionsClassLibrairie/AnswerExtensionMethods.cs b/WebApi/ExtensionsClassLibrairie/AnswerExtensionMethods.cs
new file mode 100644
index 0000000..ce9a13c
--- /dev/null
+++ b/WebApi/ExtensionsClassLibrairie/AnswerExtensionMethods.cs
@@ -0,0 +1,94 @@
+using DTOs;
+using Entities;
+using Model;
+
+namespace ExtensionsClassLibrairie
+{
+    public static class AnswerExtensionMethods
+    {
+
+        /// <summary>
+        /// convet a dto answer into a model answer
+        /// </summary>
+        /// <param name="a">the dto answer to convert</param>
+        /// <returns>the model answer that correspond</returns>
+        public static Answer ToModel(this AnswerDto a)
+        {
+            return new Answer(a.Content, a.Id);
+        }
+
+        /// <summary>
+        /// convet an entity answer into a model answer
+        /// </summary>
+        /// <param name="a">the entity answer to convert</param>
+        /// <returns>the model answer that correspond</returns>
+        public static Answer ToModel(this AnswerEntity a)
+        {
+            return new Answer(a.Content, a.Id);
+        }
+
+        /// <summary>
+        /// convet a model answer into an entity answer
+        /// </summary>
+        /// <param name="a">the model answer to convert</param>
+        /// <returns>the entity answer that correspond</returns>
+        public static AnswerEntity ToEntity(this Answer a)
+        {
+            return new AnswerEntity
+            {
+                Id = a.Id,
+                Content = a.Content
+            };
+        }
+
+        /// <summary>
+        /// convet a dto answer into an entity answer
+        /// </summary>
+        /// <param name="a">the dto answer to convert</param>
+        /// <returns>the entity answer that correspond</returns>
+        public static AnswerEntity ToEntity(this AnswerDto a)
+        {
+            return new AnswerEntity
+            {
+                Id = a.Id,
+                Content = a.Content
+            };
+        }
+
+        /// <summary>
+        /// convet a model answer into a dto answer
+        /// </summary>
+        /// <param name="a">the model answer to convert</param>
+        /// <returns>the dto answer that correspond</returns>
+        public static AnswerDto ToDto(this Answer a)
+        {
+            return new AnswerDto(a.Content, a.Id);
+        }
+
+        /// <summary>
+        /// convet an entity answer into a dto answer
+        /// </summary>
+        /// <param name="a">the entity answer to convert</param>
+        /// <returns>the dto answer that correspond</returns>
+        public static AnswerDto ToDto(this AnswerEntity a)
+        {
+            return new AnswerDto(a.Content, a.Id);
+        }
+
+        /// <summary>
+        /// equality protocole
+        /// </summary>
+        /// <param name="obj">an object</param>
+        /// <returns>
+        /// true if the object is an AnswerEntity
+        /// and the two contents are equals
+        /// (we don't care about the id because
+        /// he's set by the database
+        /// </returns>
+        public static bool Equals(this AnswerEntity a, object? obj)
+        {
+            return obj != null && obj is AnswerEntity other
+                && other.Content == a.Content;
+        }
+    }
+}
diff --git a/WebApi/ExtensionsClassLibrairie/ExtensionsClassLibrairie.csproj b/WebApi/ExtensionsClassLibrairie/ExtensionsClassLibrairie.csproj
new file mode 100644
index 0000000..0c6b8fd
--- /dev/null
+++ b/WebApi/ExtensionsClassLibrairie/ExtensionsClassLibrairie.csproj
@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\DTOs\DTOs.csproj" />
+    <ProjectReference Include="..\Entities\Entities.csproj" />
+    <ProjectReference Include="..\Model\Model.csproj" />
+  </ItemGroup>
+
+</Project>