1、
Supernova remnants: What is left after a heavy star violently explodes.
超新星遗迹: 超重星体爆炸后所剩下的残迹.
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2、
Redefining satellites Today's satellites are big and complex , which makes them costly to launch.
可升级卫星今天的人造卫星体积庞大 、 结构复杂,因此发射本很高.
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3、
