Four thieves (each stole something) were questioned. A said: each person stole only a watch; B said: I only stole a diamond; C said: I did not steal the watch; D said: some No one stole his watch. After further investigation by the police, it was found that only one person had told the truth during the interrogation. Which of the following judgments is correct? ['Everyone stole the watch.', "Everyone didn't steal the watch.", "Some people don't steal their watches.", 'B stole a diamond.']