我国青藏高原年太阳辐射总量最多的主要原因是 [ ]
A．纬度低
B．海拔高，晴天多
C．气温高
D．白昼长
答案：B
要把质量为103kg的卫星发射到地球附近的圆形轨道上，如果燃料完全燃烧产生的热量有1% 转化为卫星在轨道上运行时的动能，则需要燃烧值为q=6.4×107J/kg 的燃料多少千克？（已知地球半径R =6400km，g=9.8m/s2 ）
Water is the most 79 of all the things we eat and 80 . Not many people 81 this but it is 82 . People can last their lives 83 food for a long time , yet two or three days without water can usually make people 84 .
Many people don’t understand how much water the human body 85 . If we don’t have 86 water, we’ll feel 87 and many of us will get 88 . So you know, how important water is to us all. And we should save water any time.
