下列各组单词划线部分的字母组合哪一组发音不同。
In those days ,books could only be produced one at a time _____________.
Food safety is important. Rules _____ to stop people from food pollution.
—Why don’t we start a school magazine on line? —________
The sign means _________
--- --Who won _______prize for the “Most Beautiful Nature”photography? ------______18-year-old girl.