Ответ:

  1. You must be careful.
  2. I think that this book is useful.
  3. Shakespeare is known for writing many plays.
  4. I am very grateful to you for your help.
  5. A country which is situated in the mountains is called mountainous.
  6. Wild animals can be dangerous.
  7. Andersen wrote wonderful fairy tales.

careful — осторожный; useful — полезный; grateful — благодарный; mountainous — горный; dangerous — опасный; wonderful — чудесный.