One day, a little boy comes into a shop and says to the shop worker, "I want to buy twelve exercise books of 6 cents each and nine pencils of 10 cents each. How much is that altogether ?" The shop worker writes these numbers down on a piece of paper and thinks for a minute. Then she says, "1 dollars 62 cents." "If I give you ten dollars, how much money will I get back?" "You will get 8 dollars 38 cents for _ Here you are. These are the things you want." "No, thank you. I don't want to buy anything." The boy looks at the piece of paper and says politely, "This is my math homework. Thank you. Can I take it away?" The little boy is  _  .
bad but strong difficult but friendly stupid  but kind naughty  but clever