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【单选题】
Wildfires In just seconds, a spark or even the sun's heat alone sets off an extremely large fire. The wildfire quickly spreads, consuming the thick, dried-out plants and almost everything else in its path. What was once a forest becomes a virtual powder keg of untapped fuel. In a seemingly instantaneous burst, the wildfire overtakes thousands of acres of surrounding land, threatening the homes and lives of many in the vicinity. Fire Starters On a hot summer day, when drought conditions peak, something as small as a spark from a train car's wheel striking the track can ignite a raging wildfire. Sometimes, fires occur naturally, ignited by heat from the sun or a lightning strike. However, the majority of Wildfires are the result of human carelessness. Common causes for wildfires include: Arson Campfires Discarding lit cigarettes Improperly burning debris Playing with matches or fireworks Prescribed fires Everything has a temperature at which it will burst into flames. This temperature is called a material's flash point. Wood's flash point is 572 degrees Fahrenheit(300 ℃). When wood is heated to this temperature, it releases hydrocarbon gases that mix with oxygen in the air, combust and create fire. There are three components needed for ignition and combustion to occur. A fire requires fuel to burn, air to supply oxygen, and a heat source to bring the fuel Up to ignition temperature. Heat, oxygen and fuel form. the fire triangle. Firefighters often talk about the fire triangle when they are trying to put out a blaze. The idea is that if they can take away any one of the pillars of the triangle, they can control and ultimately extinguish the fire. After combustion occurs and a fire begins to burn, there are several factors that determine how the fire spreads. These three factors include fuel, weather and topography. Depending on these factors, a fire can quickly fizzle or turn into a raging blaze that scorches thousands of acres. Fueling the Flames Wildfires spread based on the type and quantity of fuel that surrounds it. Fuel can include everything from trees, underbrush and dry grassy fields to homes. The amount of flammable material that surrounds a fire is referred to as the fuel load. Fuel load is measured by the amount of available fuel per unit area, usually tons per acre. A small fuel load will cause a fire to burn and spread slowly, with a low intensity. If there is a lot of fuel, the fire will burn more intensely, causing it to spread faster. The faster it heats up the material around it, the faster those materials can ignite. The dryness of the fuel can also affect the behavior. of the fire. When the fuel is very dry, it is consumed much faster and creates a fire that is much more difficult to contain. Here are the basic fuel characteristics that decide how it affects a fire: Size and shape Arrangement Moisture content Small fuel materials, also called flashy fuels, such as dry grass, pine needles, dry leaves, twigs and other dead brush, burn faster than large logs or stumps(this is why you start a fire with kindling rather than logs). On a chemical level, different fuel materials take longer to ignite than others. But in a wildfire, where most of the fuel is made of the same sort of material, the main variable in ignition time is the ratio of the fuel's total surface area to its volume. Since a twig's surface area is much larger than its volume, it ignites quickly. By comparison, a tree's surface area is much smaller than its volume, so it needs more time to heat up before it ignites. As the fire progresses, it dries out the material just beyond it—heat and smoke approaching potential fuel causes the fuel's moisture to
A.
Y
B.
N
C.
NG
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【单选题】数据流图是进行软件需求分析的常用图形工具,其基本图形符号是( )。
A.
输入、输出、外部实体和加工
B.
变换、加工、数据流和存储
C.
变换、数据流、数据存储和外部实体
D.
换、数据存储、加工和数据流
【单选题】前神经孔未闭可致:()。
A.
脊髓脊膜膨出
B.
无脑儿
C.
脊髓脊柱裂
D.
头联胎
【单选题】某患者服用对髓袢升支粗段NaCl主动重吸收有抑制作用的速尿后,尿量增多,尿渗透压下降,该患者排低渗尿的原因是远曲小管和集合管
A.
对Na+主动重吸收减少
B.
对Cl-主动重吸收减少
C.
对水的通透性降低
D.
管腔外渗透压梯度降低
E.
管腔内溶质浓度增加
【单选题】有关神经管缺陷的描述错误的是
A.
致病原因可以是失去了脊索的诱导或受到导致畸形的因素的影响
B.
在神经孔或神经管没有正常闭合时出现
C.
前神经孔未闭,就会形成无脑儿
D.
后神经孔未闭,就会形成脊髓裂
E.
脊柱裂最常见于胸腰段
【单选题】某患者服用对髓袢升支粗段NaCl主动重吸收有抑制作用的呋噻米后,尿量增多,尿渗透压下降,其原因是远曲小管、集合管
A.
对Na+主动重吸收减少
B.
对Cl-主动重吸收减少
C.
对水的通透性降低
D.
管腔外渗透压梯度降低
E.
管腔内溶质浓度增加
【单选题】数据流图是进行软件需求分析的常用图形工具,其基本图形符号是()。
A.
输人、输出、外部实体和加工
B.
变换、加工、数据流和存储
C.
加工、数据流、数据存储和外部实体
D.
变换、数据存储、加工和数据流
【单选题】某患者服用对髓袢升支粗段NaCl主动重吸收有抑制作用的速尿后,尿量增多,尿渗透压下降,该患者排低渗尿的原因是远曲小管和集合管
A.
对Na+主动重吸收减少
B.
对C1-主动重吸收减少
C.
对水的通透性降低
D.
管腔外渗透压梯度降低
E.
管腔内溶质浓度增加
【单选题】某患者服用对髓袢升支粗段NaCl主动重吸收有抑制作用的速尿后,该患者排低渗尿的原因是远曲小管、集合管:
A.
对Na+主动重吸收减少
B.
对Cl-主动吸收减少
C.
对水的通透性降低
D.
管腔外渗透压梯度降低
E.
管腔内溶质浓度增加
【单选题】数据流图是进行软件需求分析的常用图形工具,其基本图形符号是( )。
A.
变化、加工、数据流、存储
B.
输入、输出、外部实体、加工
C.
加工、数据流、数据存储、外部实体
D.
数据存储、变换、数据流、加工
【单选题】数据流图是进行软件需求分析的常用图形工具,其基本图形符号是( )
A.
输入、输出、外部实体和数据处理
B.
数据处理、加工、数据流和数据存储
C.
外部实体、数据处理、数据存储、数据流
D.
外部实体、加工、输入和输出
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