【单选题】短周期元素A、B、C、D在周期表中的位置如图所示,若A的原子序数为a、最外层电子数为n,则下列关系式或说法错误的是( ) A B C D
【简答题】Additional social stresses may also occur because of the population explosion or problems arising from mass migration movements-themselves made relatively easy nowadays by modern means of transport.
【单选题】It is often ____ the passenger to know _____ demands can be made in order to get compensation as soon as possible.
【简答题】某种商品在30天内每件的销售价格P(元)与时间t(t∈N * )(天)的函数关系用如图的两条线段表示,该商品在30天内日销售量Q(件)与时间t(t∈N * )(天)之间的关系如下表: 第1天 5 15 20 30 Q件 35 25 20 10 (Ⅰ)根据提供的图象,写出该商品每件的销售价格P与时间t的函数关系; (Ⅱ)根据表中提供的数据,确定日销售量Q与时间t的一个函数关系式; (Ⅲ)求该商品的日...
【单选题】One of the most hazardous conditions a fire- fighter will ever encounter is a backdraft (also known as a smoke explosion). A backdraft can occur in the hot-smoldering phase of a fire when burning is i...
A.
has more oxygen available for combustion.
B.
has more carbon dioxide available for consumption.
C.
produces more dense gray smoke.
D.
is more likely to cause a backdraft.
【单选题】One of the most hazardous conditions a fire- fighter will ever encounter is a backdraft (also known as a smoke explosion). A backdraft can occur in the hot-smoldering phase of a fire when burning is i...
B.
open a door to allow gases to escape.
C.
make an opening at the top of the building.
D.
break a window to release carbon particles.
【简答题】Fuel gases are very combustible and can easily explode. Explosions can occur when a gas leaks from its container and reaches an ignition source, such as an open flame or spark. In the United States, m...
【单选题】在元素周期表中,A、B、C、D、X五种元素的位置关系如下图所示,已知X元素最高价氧化物的水化物化学式为H 3 XO 4 ,在这五种元素中有一种元素的原子半径在同主族元素中最小。则A元素是 [ ]
【单选题】One of the most hazardous conditions a fire- fighter will ever encounter is a backdraft (also known as a smoke explosion). A backdraft can occur in the hot-smoldering phase of a fire when burning is i...
A.
windows stained with smoke
B.
flames shooting up from the building
C.
puffs of smoke leaving the building
D.
more intense heat than usual
【单选题】监督矩阵的每行中()的位置表示相应码元之间存在的监督关系。