How many things can you see in the night sky A lot! On a clear night you might see the Moon, some planets, and thousands of sparkling stars. You can see even more with a telescope.
But scientists believe there are some things in the sky that we will never see. We won’t see them with the biggest telescope in the world, on the clearest night of the year. That’s because they’re invisible. They’re the mysterious dead stars called black holes.
As a star’s gases burn, they give off light and heat. But when the gas runs out, the star stops burning and begins to die.
As the star cools, the outer layers of the star pull in toward the center. The star squashes (挤压) into a smaller and smaller ball. If the star was very small, the star ends up as a cold, dark ball called a black dwarf. If the star was very big, it keeps squashing inward until it’s packed together tighter than anything in the universe.
Imagine if the E
A. It becomes invisible.
B. It falls to Earth.
C. It burns up all of its gases.
D. It becomes brighter and easier to see.
| 请根据下面短文回答以下各题： I’ve loved my mother’s desk since I was just tall enough to see above the top of it as mother sat doing letters. Standing by her chair, looking at the ink bottle, pens, and white paper, I decided that the act of writing must be the most wonderful thing in the world. Years later, during her final illness. Mother kept different things for my sister and brother. "But the desk," she said again, "is for Elizabeth." I never saw her angry, never saw her cry. I knew she loved me; she showed it in act ion. But as a young girl, I wanted heart-to-heart talks between mother and daughter. They never happened. And a gulf opened between us. I was "too emotional". But she lived "on the surface". As years passed and I had my own family. I loved my mother and thanked [单选题]在废水生物处理中将氨氮转化为硝酸盐氮的过程，为( )作用
A.氨化 B.消化 C.硝化 D.反硝化 [判断题]高速铁路双线电气化铁路实行垂直天窗作业时，为确保人身安全，应在设备、机具、照明、作业组织等方面采取相应措施。
A.正确 B.错误 [填空题]属于运用客车质量鉴定A类故障的是（）。
[填空题]电压互感器的铁芯是运行在（）
[单选题]746. 746.9号道岔允许的侧向通过速度为（）。
A.20km/h B.25km/h C.30km/h D.35km/h [单选题] 英文缩写DTS的含义:()。
A. 配电管理系统 B. 能量管理系统 C. 调度员仿真培训模拟 D. 自动发电控制 [填空题]国库经收处必须（）地办理各项预算收入的收纳，（）地将预算收入划转到指定收款国库。
[判断题]法维莱Eurotrol制动机，转向架EPM在正常情况下直接按比例生成制动缸预控压力，相较分配阀的模拟控制速度要快，更加准确。分配阀只是起到备用作用。
A.正确 B.错误 [判断题]在分散自律控制模式下，中心操作和车站操作方式车站（线路所）的行车工作，均由列车调度员统一指挥。
A.正确 B.错误 我来回答: 提交
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