fix issue with block placement

module/player.py

@@ -1,4 +1,5 @@
 from module import WIDTH, HEIGHT, JUMP_FORCE
+from module.block import AirBlock
 
 
 # 玩家类
@@ -8,7 +9,7 @@ class Player:
         self.y = HEIGHT // 2
         self.velocity = 0
         self.on_ground = False
-        self.selected_block = "grass"
+        self.selected_block = AirBlock
 
     def move(self, dx, dy):
         new_x = self.x + dx