4．When the great library of Alexandria burned，the story went，one book was saved．It was not a valuable book，and so a poor man who could read very little bought it for a few coins．Between its pages there was something very interesting．It was a thin paper on which was written the secret of the touchstone! The touchstone was a small pebble（卵石） that could turn any common metal into gold．The writing explained that it was lying among thousands of other pebbles that looked exactly like it．But the secret was this：The real stone would feel warm，while common pebbles were cold． So the man camped on the beach and began testing pebbles． He thought that if he picked up common pebbles and put them down again，he might pick up the same pebble hundreds of times．So，when he felt one that was cold，he threw it into the sea． He spent a whole day doing this but none of them was the touchstone． The days became weeks and the weeks into months．One day，however，he picked up a pebble and it was warm．He threw it into the sea before he realized what he had done．He had formed such a strong habit of throwing each pebble into the sea．So when the one he wanted came along，he still threw it away． So it is with chances．Unless we are careful，it's easy to fail to catch a chance when it is at hand．And it's just as easy to throw it away． 49．The poor man bought the book becauseA． A．it was very cheap B．it was of great value C．there was a secret in the book D．he wanted to find the touchstone 50．According to the story，the touchstoneC． A．is a big pebble B．feels cold C．is magic D．is gold 51．The man threw pebbles into the seaC． A．to test how far he could throw B．to practice throwing pebbles C．to avoid picking up the same pebble D．to express his disappointment 52．What does the story want to tell us？D A．Careful habits can lead to success． B．Habits can help you but also hold you back． C．Never make a decision by its look． D．Chances only visit the ready and careful mind．
