How many things can you see in the night sky? A lot!      a clear evening you might see the Moon and some planets. And thousands of sparkling stars     , too.

You can see even      with a telescope. You might see stars where you only saw dark space before. You might see that many stars look larger than others. You might see that some stars      look white are really red or blue.

But scientists believe there are some things in the sky that we               . We can’t see them with the biggest telescope in the world, even when it is the clearest night of the year. That’s         they’re invisible. They’re the mysterious dead stars called black holes. You might find          hard to imagine that stars die. After all, our Sun is a star. Year after year we see it up in the sky, burning brightly, giving us heat and light. The Sun certainly doesn’t seem          getting old or weak. But stars do burn out and die after billions of years. As a star’s gases burn, they give off light and heat. But when the gas runs        , the star stops burning and begins to die.

So the next time you stare up at the night sky, remember: there’s more in the sky than that meets the eye.        amazing space it is!

下列关于消防给水管网冲洗的说法中，错误的是（）。

A.管网冲洗的水流流速、流量不应小于系统设计的水流流速、流量

B.管网冲洗宜分区、分段进行，且管网冲洗的水流方向要与灭火时管网水流方向一致

C.管网冲洗宜设临时专用排水管道，其截面面积不小于被冲洗管道截面面积的75%

D.管网冲洗结束后，将管网内的水排除干净