不得乱扔烟蒂，护林防火人人有责 If You Must Smoke Dispose of Cigarette Butts Carefully You say“If you must”when you know that you cannot stop someone doing something that you think is wrong or stupid.) Use of differernt standard expressions不得乱扔烟蒂，护林防火人人有责 If You Must Smoke – Dispose of Cigarette Butts Carefully (You say “If you must” when you know that you cannot stop someone doing something that you think is wrong or stupid.)  Use of differernt standard expressions