由气体和尘埃物质组成的呈云雾状外表的天体是：

阅读下列短文，从每小题的三个选项中选出最佳选项。B
    Water comes from the sea, the rain and the tap. Animals, plants and human beings all need water. It is important for our daily (日常的）life. We use water to wash clothes and vegetables. We use water to cook food, make drinks, wash our face and so on. Firemen use water to put out fires. Fanners use water to grow crops. Water is useful. We mustn't waste (浪费）water. We must save water. Turn off the tap when you are brushing your teeth. Don't take a shower too long. Use the same water many times.

下面几种区域城市化典型模式中属于珠江三角洲的是（  ）

如图所示，已知AB为⊙O的直径，CD是弦，且AB⊥CD于点E．连接AC、OC、BC．

有A---H八种物质。在常温下A是无色无味气体，它可以由白色固体B和黑色固体C混合加热分解制得，反应完后C的质量和化学性质都不变。将金属D伸入盛有气体A，瓶底有少量液体E的集气瓶中，金属D剧烈燃烧，火星四射，生成黑色固体F。如把黄色粉末G点燃后放人盛A的集气瓶中，能燃烧产生蓝紫色火焰，并生成一种无色有刺激性气味的气体H。