Professor Wang is a physics teacher in Beijing. Once she was explaining to one of her classes about sound. (1)_________________________. "I have an uncle in Xinjiang," she said, "Suppose I was calling him on the phone from here and at the same time you were 25 metres away, listening to me. Who would hear me first, my uncle or you - and for what reason?" Ma Hua at once answered, "Your uncle, professor,(2)_____________________." "Good," said the professor, but then another boy raised his hand. "Yes, Li Ming?" said Professor Wang. "Of course your uncle would hear you first," Limin said, "but that's because of the time difference. (3)___________________________."