diff --git a/exercises/02_function/main.cpp b/exercises/02_function/main.cpp
index a5681be7..1de1c2a6 100644
--- a/exercises/02_function/main.cpp
+++ b/exercises/02_function/main.cpp
@@ -10,7 +10,6 @@ int main(int argc, char **argv) {
     return 0;
 }
 
-// TODO: 补全函数定义，但不要移动代码行
-// THINK: `static` 修饰函数有什么效果？
-static int add(int a, int b) {
+int add(int a, int b) {
+    // TODO: 补全函数定义，但不要移动代码行
 }
diff --git a/exercises/03_argument&parameter/main.cpp b/exercises/03_argument&parameter/main.cpp
index 5c8f8b10..764f12bd 100644
--- a/exercises/03_argument&parameter/main.cpp
+++ b/exercises/03_argument&parameter/main.cpp
@@ -2,7 +2,7 @@
 
 #include "../exercise.h"
 
-static void func(int);
+void func(int);
 
 // TODO: 为下列 ASSERT 填写正确的值
 int main(int argc, char **argv) {
diff --git a/exercises/04_static/main.cpp b/exercises/04_static/main.cpp
index d8bcc6ca..f107762f 100644
--- a/exercises/04_static/main.cpp
+++ b/exercises/04_static/main.cpp
@@ -1,12 +1,15 @@
 #include "../exercise.h"
 
-int func(int param) {
+// READ: `static` 关键字 <https://zh.cppreference.com/w/cpp/language/storage_duration>
+// THINK: 这个函数的两个 `static` 各自的作用是什么？
+static int func(int param) {
     static int static_ = param;
-    std::cout << "static_ = " << static_++ << std::endl;
-    return static_;
+    // std::cout << "static_ = " << static_ << std::endl;
+    return static_++;
 }
 
 int main(int argc, char **argv) {
+    // TODO: 将下列 `?` 替换为正确的数字
     ASSERT(func(5) == ?, "static variable value incorrect");
     ASSERT(func(4) == ?, "static variable value incorrect");
     ASSERT(func(3) == ?, "static variable value incorrect");
diff --git a/exercises/23_std_vector/main.cpp b/exercises/23_std_vector/main.cpp
index 8358a9d1..c82e7c37 100644
--- a/exercises/23_std_vector/main.cpp
+++ b/exercises/23_std_vector/main.cpp
@@ -63,7 +63,7 @@ int main(int argc, char **argv) {
             auto capacity = vec.capacity();
             vec.resize(16);
             ASSERT(vec.size() == ?, "Fill in the correct value.");
-            ASSERT(vec.capacity() == ?, "Fill in the correct identifier.");
+            ASSERT(vec.capacity() == ?, "Fill in a correct identifier.");
         }
         {
             vec.reserve(256);
diff --git a/exercises/xmake.lua b/exercises/xmake.lua
index 82b2f5d9..2f8922c7 100644
--- a/exercises/xmake.lua
+++ b/exercises/xmake.lua
@@ -1,6 +1,6 @@
 add_rules("mode.debug", "mode.release")
 set_encodings("utf-8")
-set_warnings("all", "error")
+set_warnings("all")
 set_kind("binary")
 set_languages("cxx17")