diff --git a/alien.py b/alien.py
index b98b98d..288ebd6 100644
--- a/alien.py
+++ b/alien.py
@@ -17,61 +17,65 @@ class Alien(Sprite):
         # 储存外星人的准确位置
         self.x = float(self.rect.x)
 
-        def blitme(self):
-            """在指定位置绘制外星人"""
-            self.screen.blit(self.image, self.rect)
+    def blitme(self):
+        """在指定位置绘制外星人"""
+        self.screen.blit(self.image, self.rect)
 
-        def check_edgrs(self):
-            """如果外星人位于屏幕边缘，就返回True"""
-            screen_rect = self.screen.get_rect()
-            if self.rect.right >= screen_rect.right:
-                return True
-            elif self.rect.left <= 0:
-                return True
+    def check_edgrs(self):
+        """如果外星人位于屏幕边缘，就返回True"""
+        screen_rect = self.screen.get_rect()
+        if self.rect.right >= screen_rect.right:
+            return True
+        elif self.rect.left <= 0:
+            return True
 
-            def update(self):
-                """向左或向右移动外星人"""
-                self.x += (self.ai_settings.alien_speed_factor * self.ai_settings.fleet_direction)
-                self.rect.x = self.x
+    def update(self):
+        """向左或向右移动外星人"""
+        self.x += (self.ai_settings.alien_speed_factor * self.ai_settings.fleet_direction)
+        self.rect.x = self.x
 
-        class BoosAlien(Sprite):
-            """BOOS外星人"""
 
-            def __init__(self, ai_settings, screen, health=500):
-                """初始化外星人并设置其初始位置"""
-                self.screen = screen
-                self.ai_settings = ai_settings
-                self.health = health
-                # 加载外星人图像，并设置其rect属性
-                self.image = pygame.image.load('images/boosalien.png')
-                self.rect = self.image.get_rect()
-                self.screen_rec = screen.get_rect()
-                self.rect.x = 550
-                self.rect.y = 100
-                # 储存外星人的精准位置
-                self.x = float(self.rect.x)
+class BoosAlien(Sprite):
+    """BOOS外星人"""
 
-            # #设置生命值
-            # health=100
-            def blitme(self):
-                """在指定位置绘制外星人"""
-                self.screen.blit(self.image, (self.rect.x, self.rect.y))
+    def __init__(self, ai_settings, screen, health=500):
+        """初始化外星人并设置其初始位置"""
+        self.screen = screen
+        self.ai_settings = ai_settings
+        self.health = health
+        # 加载外星人图像，并设置其rect属性
+        self.image = pygame.image.load('images/boosalien.png')
+        self.rect = self.image.get_rect()
+        self.screen_rec = screen.get_rect()
+        self.rect.x = 550
+        self.rect.y = 100
+        # 储存外星人的精准位置
+        self.x = float(self.rect.x)
 
-            def draw_health_bar(self):
-                """显示血条"""
-                # 参数依次表示：在screen上面绘制，颜色，（改图案左上角的坐标，长度和高度）
-                # 灰色的空白血条
-                pygame.draw.rect(screen, (0, 230, 0), ((380, 100), (500, 10)))
+        # #设置生命值
+        # health=100
 
-            def check_edgrs(self):
-                """如果外星人位于屏幕边缘就返回True"""
-                screen_rect = self.screen.get_rect()
-                if self.rect.right >= screen_rect.right:
-                    return True
-                elif self.rect.left <= 0:
-                    return True
+    def blitme(self):
+        """在指定位置绘制外星人"""
+        self.screen.blit(self.image, (self.rect.x, self.rect.y))
 
-            def update(self):
-                """向左向右移动外星人"""
-                self.x += (self.ai_settings.alien_speed_factor * self.ai_settings.bossalien_direction)
-                self.rect.x = self.x
+    def draw_health_bar(self, screen):
+        """显示血条"""
+        # 参数依次表示：在screen上面绘制，颜色，（改图案左上角的坐标，长度和高度）
+        # 灰色的空白血条
+        pygame.draw.rect(screen, (0, 230, 0), ((380, 100), (500, 10)))
+        # 红色的现有血条
+        pygame.draw.rect(screen, (255, 0, 0), ((380, 100), (self.health, 10)))
+
+    def check_edgrs(self):
+        """如果外星人位于屏幕边缘就返回True"""
+        screen_rect = self.screen.get_rect()
+        if self.rect.right >= screen_rect.right:
+            return True
+        elif self.rect.left <= 0:
+            return True
+
+    def update(self):
+        """向左向右移动外星人"""
+        self.x += (self.ai_settings.alien_speed_factor * self.ai_settings.bossalien_direction)
+        self.rect.x = self.x