牛棚里有6头牛，其中3头被拉到田里耕地了，现在牛棚里还剩____头牛。

依次填入下列文段横线处的句子，最恰当的一顶是 （     ）

位于百色市田东县境内的棋盘滩，因石块被水流纵横切割得整齐有序酷似棋盘而得名，_____，石块就像浮在水面。______河水冬暖夏凉，清澈见底，______在纵横交错的石块生漫步，会感到心旷神怡______。

①仿佛进入奇妙无穷的人间仙境     ②棋盘内潺潺流水常年不断

③水底的绿藻和游鱼清晰可见       ④行人踏石而过，河水不沾湿鞋底

阅读理解
(Mr. Zhang is showing Wei Fang and Li Lei a modern factory.)
Mr. Zhang: You can’t see many workers here, but you can see a lot of robots. Look, that robot has two big hands.
Wei Fang: How strong it looks!
Mr. Zhang: Yes. It does much work for us.
Li Lei: There are so many big boxes here. What are the robots doing?
Mr. Zhang: They are making fridges.
Wei Fang: How fast they are working!
Li Lei: How much time do they need to make a fridge, Mr. Zhang?
Mr. Zhang: About five minutes.
Wei Fang and Li Lei: Only five minutes! What a modern factory it is!

如图是某草原生态系中部分生物形成的食物网，请根据图分析：