diff --git a/tutorial/04_borrowing.md b/tutorial/04_borrowing.md
index 8d91f00..c4c968e 100644
--- a/tutorial/04_borrowing.md
+++ b/tutorial/04_borrowing.md
@@ -44,6 +44,7 @@ fn main() {
     let r3 = &mut s;
     r3.push_str(", world");
     println!("{}", r3);
+    println!("s is {}",s); //会发现 s 的值变了
 }
 ```