diff --git a/src/MathQuestionGenerator.java b/src/MathQuestionGenerator.java
index 87348f6..fd2a78b 100644
--- a/src/MathQuestionGenerator.java
+++ b/src/MathQuestionGenerator.java
@@ -309,6 +309,22 @@ public class MathQuestionGenerator {
      * @return 切换是否成功
      */
     private static boolean handleSwitchCommand(String command) {
+        // 【人工修复】修复字符串越界风险，添加长度检查
+        // 修改前：command.substring(3) 可能抛出StringIndexOutOfBoundsException
+        // 修改后：先检查命令长度，确保安全访问
+        if (command.length() < 3) {
+            System.out.println();
+            System.out.println("✗ 请输入小学、初中和高中三个选项中的一个");
+            System.out.println("按回车键继续...");
+            System.out.flush();
+            try {
+                @SuppressWarnings("unused")
+                int readResult = System.in.read();
+            } catch (IOException e) {
+                // 忽略读取错误
+            }
+            return false;
+        }
         String targetGrade = command.substring(3).trim();
 
         if (targetGrade.equals("小学") || targetGrade.equals("初中") || targetGrade.equals("高中")) {
@@ -517,8 +533,14 @@ public class MathQuestionGenerator {
                     String line;
                     while ((line = reader.readLine()) != null) {
                         if (line.matches("\\d+\\.\\s+.+")) {
-                            String question = line.substring(line.indexOf(".") + 1).trim();
-                            historyQuestions.add(question);
+                            // 【人工修复】修复字符串越界风险，添加安全检查
+                            // 修改前：line.indexOf(".") 可能返回-1，导致substring(-1+1)问题
+                            // 修改后：先检查indexOf结果，确保安全访问
+                            int dotIndex = line.indexOf(".");
+                            if (dotIndex != -1 && dotIndex + 1 < line.length()) {
+                                String question = line.substring(dotIndex + 1).trim();
+                                historyQuestions.add(question);
+                            }
                         }
                     }
                 } catch (IOException e) {
diff --git a/src/PrimaryQuestionGenerator.java b/src/PrimaryQuestionGenerator.java
index a55d49e..d592f57 100644
--- a/src/PrimaryQuestionGenerator.java
+++ b/src/PrimaryQuestionGenerator.java
@@ -24,13 +24,12 @@ public class PrimaryQuestionGenerator extends AbstractQuestionGenerator {
             // 随机添加括号，确保括号内也有运算符
             if (i < operands.length - 1 && random.nextBoolean()) {
                 question.append(" ").append(op).append(" (").append(operands[i]);
-                if (i + 1 < operands.length) {
-                    op = BASIC_OPERATORS[random.nextInt(BASIC_OPERATORS.length)];
-                    question.append(" ").append(op).append(" ").append(operands[i + 1]).append(")");
-                    i++; // 【人工修复】修复数组越界风险，手动增加i以跳过已处理的操作数
-                } else {
-                    question.append(")");
-                }
+                // 【人工修复】修复逻辑错误，移除多余的边界检查
+                // 修改前：if (i + 1 < operands.length) 是多余的，因为外层条件已经确保i < operands.length - 1
+                // 修改后：直接处理i+1位置的操作数，因为条件已经保证其存在
+                op = BASIC_OPERATORS[random.nextInt(BASIC_OPERATORS.length)];
+                question.append(" ").append(op).append(" ").append(operands[i + 1]).append(")");
+                i++; // 手动增加i以跳过已处理的操作数
             } else {
                 question.append(" ").append(op).append(" ").append(operands[i]);
             }