如图，以O为位似中心将四边形ABCD放大后得到四边形A′B′C′D′，若OA=4，OA′=8，则四边形ABCD和四边形A′B′C′D′的周长的比为（　　）

科学家用辐射的方法处理普通叶型豌豆，得到了豌豆半无叶型性状的突变体，半无叶型是受基因a控制的，呈完全隐性，该基因与子叶颜色基因都位于第一号染色体上，且子叶黄色Y对绿色y为显性。下列说法错误的是    （）

    I' m David, a baby penguin (企鹅). It is snowing outside. I am staying____my nest (~) and waiting for my parents. They went out yesterday to ____food for me. I feel so cold and hungry now because we don't have any food at all. In the last few years,____developed the economy (发展经济), but they forgot the____

    They cut many trees down and ____ lots of factories. The____ from those factories soon changed the climate (改变气候). So it's harder for my parents to find food. What's worse,____ penguins died because of the climate change. But now, people in the world seem to know their mistakes (错误) and begin to do something to save the world. I think we can live a better life in the____

根据以上信息，结合所学知识，对划线部分的现象作出解释。

如图所示甲、乙是两种声音的波形图，从图形可知： ____ 图是乐音的波形 ____，图是噪声的波形．