You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: SCIENCE FICTION 
Clue: A recent re-issue of this Sir Arthur Conan Doyle novel includes an introduction by Michael Crichton
the lost world

Category: DEMOGRAPHICS 
Clue: In 2005 the World Health Organization appropriately decided to stop hiring people who do this
smoke

Category: LANDMARKS 
Clue: Plans are for steel cables to temporarily replace the over 800 tons of lead that counterbalance it

the leaning tower of pisa