【单选题】Why does the author mention refrigeration in paragraph 6?
A.
To show how the steam engine contributed to refrigeration
B.
To illustrate the standard of living of North America and Europe
C.
To give an example of an innovation that expanded markets
D.
To argue that refrigeration was the most important invention of the time
【简答题】发光二极管简称 ,经常使用的发光二极管管脚引线较长者为 ,引线较短的为 。
【单选题】关于物体的明暗规律说法正确的是
D.
物体的明暗变化与物体的结构无关物体的明暗变化与物体的结构无关
【单选题】If a boiler is isolated from the steam-using system, how must it be kept?
A.
ln closed dry storage.
B.
Completely full of treated water.
C.
Under a low steam pressure
【简答题】Steam cracking is endothermic. How to supply the heat needed?
【简答题】How is steam generated in a fossil-fueled power plant?