I didn't get up earlier as usual last Sunday. In the morning having finished my homework, I do some washing．Then I telephoned one of my classmates and invited them to see a film．But unfortunately, when we got to the cinema, we founded all the tickets had sold out．We had to go back to school or play football．After that, we were about to go to home when we saw our English teacher, Mr. Li, coming towards us．Tom and I asked him some questions about what to learn English well．He told us we had made great progresses in English．He also suggested that we read more and write more．We promised him that we would follow our advice．

论述音准曲线的成因。