travelling green

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Across
  1. 4. why does weight matter when planes are flying?
  2. 6. plant matter
  3. 7. walking is .... For the environment than cars are.
Down
  1. 1. how many people travel by plane per year?
  2. 2. which one is better for the environment:bus or plane?
  3. 3. which of these is a maglev train: heavy-rail or light-rail?
  4. 5. what do plug-in cars run on?