diff --git a/unit04_public_key/lab/sample_ans.md b/unit04_public_key/lab/sample_ans.md
index 428734c..715b9da 100644
--- a/unit04_public_key/lab/sample_ans.md
+++ b/unit04_public_key/lab/sample_ans.md
@@ -344,6 +344,8 @@ The curves are:
   brainpoolP512t1: RFC 5639 curve over a 512 bit prime field
   SM2       : SM2 curve over a 256 bit prime field
 ```
+
+## C.5
 The commands are:
 
 ```