17、Time spent in a bookshop can be enjoyable. If you go to a _ _ 21 _ _ shop, no assistant will come near to you and say, "Can I help you?" You needn't buy anything you don't want. You may try to find out _ _ 22 _ _ the book you want is. But if you fail, the assistant will lead you there and then he will go away. It seems that he is not interested in selling any book at all.
There is a story which tells us about a good shop. A medical student _ _ 23 _ _ a very useful book in the shop, but it was too expensive for him to buy. He couldn't get it from the library, either. So every afternoon, he went there to read _ _ 24 _ _ at a time. One day, however, he couldn't find the book from its usual place and was leaving when he saw an assistant signing to him. To his surprise, the assistant pointed to the book _ _ 25 _ _ , "I put it there so as not to be sold out," said the assistant. Then he left the student to go on with his reading.