I phone

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Across
  1. 2. a single thing
  2. 3. guess
  3. 4. the main offices of an organization such as the army, the police, or a business company
  4. 7. difficult to understand or find an answer to
  5. 8. relating to the whole world
  6. 9. join together to make a single thing
Down
  1. 1. to make goods in large numbers, usually in a factory using machines
  2. 3. the process of putting together the parts of a machine or structure
  3. 5. a person whose job is to design or build machines, engines, or electrical equipment
  4. 6. a company, person, etc. that provides things