Ответ:

  1. Look, there’s a(n) UFO in the sky!
  2. Charles has a(n) hobby; he likes collecting old bicycles.
  3. Mary often goes ghost hunting in haunted houses.
  4. That’s not a UFO in the sky; it’s a weather balloon.
  5. Martin sometimes finds valuable jewellery when he goes metal detecting.
  6. I don’t believe in UFOs; they are just optical illusions.
  7. We look for storms, so we can go storm chasing.
  8. Janet likes upcycling; she uses parts from old televisions to make them.

Ответ: 1) UFO; 2) hobby; 3) ghost hunting; 4) weather balloon; 5) metal detecting; 6) optical illusions; 7) storm chasing; 8) upcycling.