diff --git a/alien.py b/alien.py
index 1f6ba0f..2c65aa7 100644
--- a/alien.py
+++ b/alien.py
@@ -29,4 +29,5 @@ class Alien(Sprite):
     def check_edges(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:
\ No newline at end of file
+        if self.rect.right >= screen_rect.right:
+            return True
\ No newline at end of file