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When the Great Library of Alexandria burned，the story goes that one book was saved．But nobody thought it was a v__1__ book．A poor man，who could read a little，bought it for a few coins．

The book wasn't very interesting．but between its pages there was something very interesting i__2__．It was a thin strip of vellum（羊皮纸）on which as written the secret of the “Touchstone”!

The touchstone was a small pebble（卵石）that could t__3__ any common metal into pure gold．The writing e__4__ that it was lying among thousands of other pebbles that looked exactly like it．But the secret was that the real stone would feel w__5__，while ordinary pebbles were cold．

So the man camped on the seashore and began testing pebbles．He knew that if he picked up ordinary pebbles and threw them down again b__6__ they were cold，he might pick up the same pebble hundreds of t__7__．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．Y_8__ he went on and on this way．

One day，however，about mid-afternoon，he picked up a pebble and it was warm．He threw it into the sea b__9_ he realized what he had done．He had formed such a strong habit of throwing each pebble into the sea that when the one he wanted came along，he still threw it away．

So it is with opportunity（机会）．U__10__ we are careful，it's easy to fail to recognize an opportunity when it is in hand．