diff --git a/source/02_language_guide/09_Structures_And_Classes.md b/source/02_language_guide/09_Structures_And_Classes.md
index 9c63ad50..371added 100755
--- a/source/02_language_guide/09_Structures_And_Classes.md
+++ b/source/02_language_guide/09_Structures_And_Classes.md
@@ -32,6 +32,10 @@ Swift 中结构体和类有很多共同点。两者都可以：
 
 类支持的附加功能是以增加复杂性为代价的。作为一般准则，优先使用结构体，因为它们更容易理解，仅在适当或必要时才使用类。实际上，这意味着你的大多数自定义数据类型都会是结构体和枚举。更多详细的比较参见 [在结构和类之间进行选择](https://developer.apple.com/documentation/swift/choosing_between_structures_and_classes)。
 
+> 注意
+> 
+> 类和 actors 共享很多特性。更多信息请参见 [并发](./18_Concurrency.md)。
+
 ### 类型定义的语法 {#definition-syntax}
 
 结构体和类有着相似的定义方式。你通过 `struct` 关键字引入结构体，通过 `class` 关键字引入类，并将它们的具体定义放在一对大括号中：
diff --git a/source/02_language_guide/18_Concurrency.md b/source/02_language_guide/18_Concurrency.md
new file mode 100644
index 00000000..7f9bb373
--- /dev/null
+++ b/source/02_language_guide/18_Concurrency.md
@@ -0,0 +1 @@
+# aasas
diff --git a/source/02_language_guide/18_Type_Casting.md b/source/02_language_guide/19_Type_Casting.md
similarity index 100%
rename from source/02_language_guide/18_Type_Casting.md
rename to source/02_language_guide/19_Type_Casting.md
diff --git a/source/02_language_guide/19_Nested_Types.md b/source/02_language_guide/20_Nested_Types.md
similarity index 100%
rename from source/02_language_guide/19_Nested_Types.md
rename to source/02_language_guide/20_Nested_Types.md
diff --git a/source/02_language_guide/20_Extensions.md b/source/02_language_guide/21_Extensions.md
similarity index 100%
rename from source/02_language_guide/20_Extensions.md
rename to source/02_language_guide/21_Extensions.md
diff --git a/source/02_language_guide/21_Protocols.md b/source/02_language_guide/22_Protocols.md
similarity index 100%
rename from source/02_language_guide/21_Protocols.md
rename to source/02_language_guide/22_Protocols.md
diff --git a/source/02_language_guide/22_Generics.md b/source/02_language_guide/23_Generics.md
similarity index 100%
rename from source/02_language_guide/22_Generics.md
rename to source/02_language_guide/23_Generics.md
diff --git a/source/02_language_guide/23_Opaque_Types.md b/source/02_language_guide/24_Opaque_Types.md
similarity index 100%
rename from source/02_language_guide/23_Opaque_Types.md
rename to source/02_language_guide/24_Opaque_Types.md
diff --git a/source/02_language_guide/24_Automatic_Reference_Counting.md b/source/02_language_guide/25_Automatic_Reference_Counting.md
similarity index 100%
rename from source/02_language_guide/24_Automatic_Reference_Counting.md
rename to source/02_language_guide/25_Automatic_Reference_Counting.md
diff --git a/source/02_language_guide/25_Memory_Safety.md b/source/02_language_guide/26_Memory_Safety.md
similarity index 100%
rename from source/02_language_guide/25_Memory_Safety.md
rename to source/02_language_guide/26_Memory_Safety.md
diff --git a/source/02_language_guide/26_Access_Control.md b/source/02_language_guide/27_Access_Control.md
similarity index 100%
rename from source/02_language_guide/26_Access_Control.md
rename to source/02_language_guide/27_Access_Control.md
diff --git a/source/02_language_guide/27_Advanced_Operators.md b/source/02_language_guide/28_Advanced_Operators.md
similarity index 100%
rename from source/02_language_guide/27_Advanced_Operators.md
rename to source/02_language_guide/28_Advanced_Operators.md