Crossword Quiz

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Across
  1. 5. Creator of first true combustion engine
  2. 6. Earliest known chemical explosive
  3. 7. Flammable gaseous fuel
Down
  1. 1. branch of physics that deals with heat, work, and temperature
  2. 2. Moving component contained by the cylinder
  3. 3. Space devoid of (without) matter
  4. 4. Popular combustion engine type