diff --git a/README.md b/README.md
index fa5d800..86cdd72 100644
--- a/README.md
+++ b/README.md
@@ -4615,6 +4615,8 @@ gcc echo_EPETserv.c -o serv
 
 ### 18.1 理解线程的概念
 
+#### 18.1.1 引入线程背景
+