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on 3. without 4. on 5. In 6. At。 1. Paper can be made of silk, cotton, bamboo and wood. ___________ 2. A new oil field(油田 ) was invented three days later. ___________ 3. A few people learned to read because the books were expensive and rare at that time. ___________ 4. The first printing books were made by putting ink on a wooden block and holding the paper against it. ___________ 5. Printing was developed greatly and books could be produced more quick and cheap. ____