17．You stayed at your friends' house when you participated in a business seminar in Australia．You left a file with important documents in your room．
Task: Write a letter to your friend, describing the file and ask him/her to return it to you by post．
18．You have recently made a purchase from the local department store．However, when you arrived home, you found a fault with it．Write a letter to the manager, say what the product is, explain the problem and say what you'd like to be done about it．