完形填空。 One day a pig went to the stable (马棚) to 1 a good friend, an old horse, and was going to 2 there for the night. Night came and it was time 3 sleep. The pig went into the straw heap (稻草堆) and lay comfortably (舒服地). A long time 4 , but the horse was still 5 there and did not move. So the pig asked the horse 6 he did not go to sleep. 'Standing like this is the beginning of sleeping.' answered the 7 .The pig found it 8 to believe (相信) and said, 'How can you stand there sleeping? It is not comfortable at all.' The horse answered, 'Comfort is your habit (习性). 9 horses, we have the habit of running quickly. So we are always ready to run quickly even if (即使) we are 10 . (     )1. A. look (     )2. A. left (     )3. A. by (     )4. A. passed (     )5. A. standing (     )6. A. what (     )7. A. animals (     )8. A. hardly (     )9. A. While (     )10. A. sleep B. see B. sit B. on B. pass B. stands B. why B. pig B. easily B. For B. asleep C. watch C. lay C. to C. past C. sitting C. when C. horse C. difficult C. As C. slept D. look at D. stay D. with D. was passed D. lying D. which D. heap D. easy D. Like D. to sleep