①草原辽阔  ②气候条件适合  ③人口多，羊毛、羊肉需求量大  ④没有食肉猛兽

①用刻度尺和三角板测量出玻璃管底面直径D，并把数据记录在表格中；

②向玻璃管内装入适量的沙子，使玻璃管能竖直地漂浮在水中，用刻度尺测出h₁（如图甲），并将数据记录在表格中；

③从水中取出试管，擦干后用调节好的天平称出玻璃管和沙子的总质量m₁，并将数据记录在表格中；

④再向玻璃管内添加沙子，使玻璃管仍能竖直地漂浮在水中，用刻度尺测出h₂（如图乙）；用天平称出玻璃管和沙子的总质量m₂，并将数据记录在表格中；

⑤根据公式p= $\frac{F}{S}$ =    ▲     和测量数据，计算出压强p₁和p₂，并将数据记录在表格中.

请根据以上叙述回答下列问题：

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　  Do you carry too much on the way to school or home? Don’t worry．Try e-readers (电子阅读器) and say goodbye to your heavy schoolbag．
   An e-reader has the memory space to hold hundreds of books．So people want to (A)扔掉沉书包 and read with small, light e-readers．For example，Cushing Academy，a high school in Massachusetts，USA，replaced (替换) most of the 20，000 books in (B) its library last summer．Teachers and students will use e-readers instead．
   Most e-readers are thin and weigh less than 500g．They can download (下载) an e-book in 60 seconds．“It’s (C) so easy．You can have a lot of books right at your fingers!” said Meghan Chensusky．
   Chinese schoolchildren are also trying e-readers．At the Shanghai World Expo (世博会)，an e-schoolbag is now on show．It is a special e-reader．Students can use it to download textbooks from the school servers (服务器)．(D)It can also send and receive homework．Some Schools in Beijing and Shanghai have tried this e-schoolbag for a few years．“It’s excellent．I (E)don’t have to carry a heaw schoolbag anymore，”said Xiao Qi，15，Beijing．
   New e-readers are not just for reading．They have Wi-Fi and multimedia (无线电视和多媒体)．Parents worry that these may hurt their children’s study habits． “I think Wi-Fi is not necessary for kids，”said Zeng Wenwen，43， Beijing．