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To be unstable is to be（)
A、usual
B.unsteady
C.complete
请帮忙给出正确答案和分析，谢谢！
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更多“To be unstable is to be（)A、usualB.unsteadyC.complete请帮忙给出正确答案和分析，谢谢！……”相关的问题
第2题
不稳定型心绞痛( Unstable Angina)属急性冠脉综合征，其特征为心肌氧的供需失衡。常见原因是动脉粥样斑块破裂，产生非闭塞性血栓。可有心肌坏死生化标志物升高。（）
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第3题
Unlike free phrases, the structure of an idiom is to a large extent .（)
A. changeable
B. unchangeable
C. unstable
D. unfixed
请帮忙给出正确答案和分析，谢谢！
A. changeable
B. unchangeable
C. unstable
D. unfixed
请帮忙给出正确答案和分析，谢谢！
第4题
Radiocarbon DatingNowadays scientists can answer many questions about the past through a t
Radiocarbon Dating
Nowadays scientists can answer many questions about the past through a technique called radiocarbon(放射性碳), or carbon-14, dating. One key to understanding how and why something happened is to discover when it happened.
Radiocarbon dating was developed in the late 1940s by physicist Willard F. Libby at the University of Chicago. An atom of ordinary carbon, called carbon-12, has six protons(质子) and six neutrons(中子) in its nucleus. Carbon-14, or C-14, is a radioactive, unstable form. of carbon that has two extra neutrons(原子核). It returns to a more stable form. of carbon through a process called decay(衰减). This process involves the loss of the extra neutrons and energy from the nucleus.
In Libby's radiocarbon dating technique, the weak radioactive emissions(放射) from this decay process are counted by instruments such as a radiation detector and counter. The decay rate is used to determine the proportion of C-14 atoms in the sample being dated.
Carbon-14 is produced in the Earth's atmosphere when nitrogen(氮)-14, or N-14, interacts with cosmic rays(宇宙射线). Scientists believe since the Earth was formed, the amount of nitrogen in the atmosphere has remained constant. Consequently, C-14 formation is thought to occur at a constant rate. Now ratio of C-14 to other carbon atoms in the atmosphere is known. Most scientists agree that this ratio is useful for dating items back to at least 50,000 years.
All life on Earth is made of organic molecules(分子) that contain carbon atoms coming from the atmosphere. So all living things have about the same ratio of C-14 atoms to other carbon atoms in their tissues(组织). Once an organism(有机体) dies it stops taking in carbon in any form, and the C-14 already present begins to decay. Over time the amount of C-14 in the material decreases, and the ratio of C-14 to other carbon atoms goes down. In terms of radiocarbon dating, the fewer C-14 atoms in a sample, the older that sample is.
Nowadays many scientists depend on radiocarbon for dating age-old objects.
A．Right
B．Wrong
C．Not mentioned
请帮忙给出正确答案和分析，谢谢！
Radiocarbon Dating
Nowadays scientists can answer many questions about the past through a technique called radiocarbon(放射性碳), or carbon-14, dating. One key to understanding how and why something happened is to discover when it happened.
Radiocarbon dating was developed in the late 1940s by physicist Willard F. Libby at the University of Chicago. An atom of ordinary carbon, called carbon-12, has six protons(质子) and six neutrons(中子) in its nucleus. Carbon-14, or C-14, is a radioactive, unstable form. of carbon that has two extra neutrons(原子核). It returns to a more stable form. of carbon through a process called decay(衰减). This process involves the loss of the extra neutrons and energy from the nucleus.
In Libby's radiocarbon dating technique, the weak radioactive emissions(放射) from this decay process are counted by instruments such as a radiation detector and counter. The decay rate is used to determine the proportion of C-14 atoms in the sample being dated.
Carbon-14 is produced in the Earth's atmosphere when nitrogen(氮)-14, or N-14, interacts with cosmic rays(宇宙射线). Scientists believe since the Earth was formed, the amount of nitrogen in the atmosphere has remained constant. Consequently, C-14 formation is thought to occur at a constant rate. Now ratio of C-14 to other carbon atoms in the atmosphere is known. Most scientists agree that this ratio is useful for dating items back to at least 50,000 years.
All life on Earth is made of organic molecules(分子) that contain carbon atoms coming from the atmosphere. So all living things have about the same ratio of C-14 atoms to other carbon atoms in their tissues(组织). Once an organism(有机体) dies it stops taking in carbon in any form, and the C-14 already present begins to decay. Over time the amount of C-14 in the material decreases, and the ratio of C-14 to other carbon atoms goes down. In terms of radiocarbon dating, the fewer C-14 atoms in a sample, the older that sample is.
Nowadays many scientists depend on radiocarbon for dating age-old objects.
A．Right
B．Wrong
C．Not mentioned
请帮忙给出正确答案和分析，谢谢！
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