以下是某同学测定煤油的密度的一些实验步骤：

（1）用天平测出空矿泉水瓶的质量m₀；

（2）在矿泉水瓶里装满水，用天平测出它们的总质量m₁；

（3）用矿泉水瓶装满煤油，用天平测出它们的质量m₂；

（4）用量筒测出矿泉水瓶里所盛煤油的体积V；

（5）计算煤油的密度．

这些步骤中可省去的是（　　）

正如当初无人能预测1450年的印刷术、1750年的蒸汽机、1950年的晶体管会带来何等影响，而今我们仍然无法预测3D打印将在未来漫长的时间里如何改变世界。这说明（   ）

    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____