发生接地故障时，特有的电气量是零序电压和电流。

在FOR-ENDFOR循环体的任何位置上都可以使用 【8】 语句用于重新进行下一次再循环。

下列有关单倍体的叙述，正确的是[ ]

A．体细胞中包含一个染色体组的个体

B．体细胞中含有奇数染色体数目的个体

C．体细胞中含有本物中配子染色体数目的个体

D．体细胞中含有奇数染色体组数目的个体

肝脓肿的声像图特征是（）

A.肝脏回声增强，细密，肝内管道分布走向不明显

B.肝脏萎缩，尾状叶增大，肝回声增粗，稍增强，表面不光滑，有结节感

C.肝实质内出现低回声性至无回声性区，边缘不整齐，欠规则

D.肝脏左叶增大，右叶萎缩，肝实质被网状高回声分隔，呈"地图样"改变

E.肝内一个或多个圆形或椭圆形占位，呈等回声或弱回声，多有声晕

下列问诊内容正确的是 （）

A．你心前区痛反射到左肩吗

B．你右上腹痛反射到右肩痛吗

C．解大便有里急后重吗

D．你觉得最主要的是哪里不适

E．腰痛时反射到大腿内侧痛吗

All animals must rest, but do they really sleep as we know it The answer to this question seems obvious. If an animal regularly stops its activities and stays quiet and unmoving—if it looks as though it is sleeping—then why not simply assume that it is in fact sleeping But how can observers be sure that an animal is sleeping

They can watch the animal and notice whether its eyes are open or closed, whether it is active or lying quietly, and whether it responds to light or sound. These factors are important clues, but they often are not enough. Horses and cows, for example, rarely close their eyes, and fish and snakes cannot close them. Yet this does not necessarily mean that they do not sleep. Have you ever seen a cat dozing with an eye partly open Even humans have occasionally been observed to sleep with one or both eyes partially open. Animals do not necessarily lie down to sleep either. Elephants, for example, often sleep standing up, with their tusks resting in the fork of a tree. Finally, while "sleeping" animals often seem unaware of changes in the sounds and light and other stimuli around them, that does not really prove they are sleeping either.

Observations of animal behavior alone cannot fully answer the question of whether or not animals sleep. The answers come from doing experiments in "sleep laboratories" using a machine called the electroencephalograph (EEC). The machine is connected to animals and measures their brain signals, breathing, heartbeat, and muscle activity. The measurements are different when the animals appear to be sleeping than when they appear to be awake. Using the EEC, scientists have confirmed that all birds and mammals studied in laboratories do sleep. There is some evidence that reptiles, such as snakes and turtles, do not truly sleep, although they do have periods of rest each day, in which they are quiet and unmoving. They also have discovered that some animals, like chimpanzees, cats, and moles (who live underground), are good sleepers while others, like sheep, goats, and donkeys, are poor sleepers. Interestingly, the good sleepers are nearly all hunters with resting places that are safe from their enemies. Nearly all the poor sleepers are animals hunted by other animals: they must always be watching for enemies, even when they are resting.

How can researchers in "sleep laboratories" tell that the animals they are observing are asleep or not（）

A. They see if the animals respond to light and sound

B. They do this by observing changes in the animals’ brain signals, breathing, heartbeat, and muscle activity

C. They see if the animals’ eyes are closed

D. They can tell this by seeing if the animals lie down or not