Ответ:

  1. Cars are more expensive than bikes.
  2. Fruit is better for your health than fast food.
  3. History isn't as difficult as Maths.
  4. Is English easier than Turkish?
  5. Spain is usually hotter than the UK.
  6. The white shirt is as nice as the blue one!

Правило: после than используется сравнительная степень, а в конструкции as ... as — обычная форма прилагательного.