diff --git a/alien.py b/alien.py
index 8a115c0..379476b 100644
--- a/alien.py
+++ b/alien.py
@@ -27,4 +27,5 @@ class Alien(Sprite):
         self.screen.blit(self.image, self.rect)
 
     def check_edges(self):
-        """如果外星人位于屏幕边缘，就返回True"""
\ No newline at end of file
+        """如果外星人位于屏幕边缘，就返回True"""
+        screen_rect = self.screen.get_rect()
\ No newline at end of file