题目内容：

缺词填空

One day a pig went to the stable to see his good friend， an old horse， and was going to stay t 1.  for the night. Night came and it was time f  2.  sleep. The pig went into the straw heap and lay comfortably.

A long time p 3.     ， but the horse was s   4.   standing there and did not move. So the pig asked the horse w 5.    he did not go to sleep. “Standing like this is the beginning of sleep.” answered the horse. The pig found it h  6.  to believe and said， “How can you s   7.   there sleeping? It is not comfortable at a 8.  .” The horse answered， “Comfortable is your habit. A 9.   horses， we have the habit of r 10.  quickly. So we are always ready to run quickly even if we are asleep.”