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问题 多项选择题

在三相交流电路中，关于相电压与线电压、相电流与线电流的关系，下面说法正确的是（）。

A、在△形连接时，负载上的线电流等于相电流

B、在△形连接时，负载上的线电压等于相电压

C、在Y形连接时，负载上的线电流等于相电流

D、在Y形连接时，负载上的线电压等于相电压

答案

参考答案：B, C

单项选择题

Evidences of Human History


In the study of human history, there are many points that require study and research; there is one very important and interesting aspect to pay attention to, that is, the use of left or right hand in ancient humans’ activities. There has been some evidence which archaeologists have noticed and studied. What is more, many archaeological records—paintings, drawings, and carvings of humans engaged in activities involving the use of their hand—indicate that humans have been predominantly right-handed for more than 5000 years. These archaeological artworks are found almost all around the world, and though they were found to have been made in different times and places, there are many similar or identical features concerning hand use among them. In ancient Egyptian artworks, for example, the right hand is depicted as the dominant one in about 90 percent of the examples. What is more, in the archaeological artworks unearthed in Henan province, China has shown over 85 percent of the use of the right hand in manufacturing.
  • (A) [■] Fracture or wear patterns on tools also indicate that a majority of ancient people were right-handed. In some experts’ theories, they also find that some patterns and styles can reveal the use of the right hand or the left hand.
    Cro-Magnon cave paintings of some 27000 years ago commonly show outlines of human hands made by placing one hand against the cave wall and applying paint with the other.
  • (B) [■] With few exceptions, the left hands of Cro-Magnons are displayed on cave walls, indicating that the paintings were usually done by right-handers.
  • (C) [■] This point can also be reflected in modern life. If you like, imagine the general gesture of painting or doing anything in your daily life, you will find the general features and styles of your actions, which can reflect your habit of hand use, and furthermore try to find a friend or someone else who uses the other hand and compare with his or her habits, the difference will be very clear and obvious.
    Besides the above archaeological artworks in the study of ancient human beings’ hand usage, there are also other kinds of evidence in this field, at first the anthropological evidence can push the record of handedness in early human ancestors back to at least 1.4 million years ago.
  • (D) [■] Important evidence comes from the flaking patterns of stone cores used in tool making, and the implements flaked with a clockwise motion (indicating a right-handed toolmaker) can be found much more than those flaked with a counter-clockwise rotation (indicating a left-handed toolmaker). That means usually a right handed person chose the clockwise direction to make tools while a left handed man chose the counter-clockwise direction to make tools.
    Even scratches found on fossil human teeth offer clues. Ancient people are thought to have cut meat into strips by holding it between their teeth and slicing it with stone knives, as do the present-day Inuit. Occasionally the knives slip and leave scratches on the users’ teeth. Scratches made with a left-to-right stroke direction (by right-handed toolmaker) are more common than scratches in the opposite direction (by left-handed toolmaker).
    Still more evidence comes from cranial morphology: scientists think that physical differences between the right and left sides of the interior of the skull indicate subtle physical differences between the two sides of the brain. The variation between the hemispheres corresponds to which side of the body is used to perform specific activities. Such studies, as well as studies of tool use, indicate that right-or left-sided dominance is not exclusive to modern Homosapiens. Populations of Neanderthals, such as Homo Erectus and Homo Habilis, seem to have been predominantly right-handed, almost the same situation as ours today.

The author’s description of evidence concerning handedness mentions all of the following EXCEPT ______.

A．ancient artwork

B．asymmetrical skulls

C．studies of tool use

D．fossilized hand bones
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单项选择题 A1/A2型题

心室充盈过程中的主要阶段是（）

A.心房收缩期

B.等容收缩期

C.等容舒张期

D.快速充盈期

E.快速射血期
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