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Nitrogen is the most plentiful gas in the atmosphere.A．waterB．earthC．bodyD．air

Nitrogen is the most plentiful gas in the atmosphere.

A．water

B．earth

C．body

D．air

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发布时间：2020-10-20

更多“Nitrogen is the most plentiful gas in the atmosphere.A．waterB．earthC．bodyD．air”相关的问题

第1题

As viewed from space, the Earth's distinguishing characteristics are its blue waters and w

hite clouds. Enveloped by an ocean of air consisting of 78% nitrogen and 21% oxygen, the planet is the only one in our solar system known to harbor life. Circling the Sun at an average distance of 149 million km (93 million miles), the Earth is the third planet from the Sun and the fifth largest planet in the solar system. Its rapid and molten nickel-iron core give rise to an extensive magnetic field which, coupled with the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and other stars. Most meteors burn up in the Earth's atmosphere before they can strike the surface. The planet's active geological processes have left no evidence of the ancient pelting it almost certainly received soon after it was formed. The Earth has a single natural satellite-the Moon.

Approximately how much of the Earth's atmosphere is nitrogen？

A．One-fourth

B．One-half

C．Three-fourths

D．All of it

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第2题

Mineral deficiencies can often be detected by specific symptoms such as chlorosis（loss of

Mineral deficiencies can often be detected by specific symptoms such as chlorosis(loss of chlorophyll resulting in yellow or white leaf tissue), necrosis(isolated dead patches), anthocyanin formation(development of deep red pigmentation of leaves or stem), stunted growth, and development of woody tissue in an herbaceous plant. Soils are most commonly deficient in nitrogen and phosphorus. Nitrogen-deficient plants exhibit many of the symptoms just described. Leaves develop chlorosis; stems are short and slender; and anthocyanin discoloration occurs on stems, petioles, and lower leaf surfaces. Phosphorus-deficient plants are often stunted, with leaves turning a characteristic dark green, often with the accumulation of anthocyanin. Typically, older leaves are affected first as the phosphorus is mobilized to young growing tissue. Iron deficiency is characterized by chlorosis between veins in young leaves.

The word "exhibit" in the passage is closest in meaning to

A．fight off

B．show

C．cause

D．spread

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第3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

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第4题

There is now no doubt that the world is getting warmer. Data from both the Southern and No

rthern Hemispheres(地球的半球)shows a(n)【C1】______trend in average temperatures over the【C2】______hundred years. At the moment most scientists are not prepared to stick their necks out and【C3】______a cause to this trend. It is possible that it represents a natural climatic change caused by a【C4】______increase in the sun's radiation output. But these same scientists are【C5】______aware that recent temperature changes are at the limit of known natural【C6】______: it seems increasingly likely that the cause is a(n)【C7】______greenhouse effect.

The basic theory of the greenhouse effect is quite simple. The earth's atmosphere consists【C8】______of oxygen and nitrogen,【C9】______there are small concentrations of various "greenhouse" gases-【C10】______carbon dioxide, water vapor, and methane(沼气)-- which play a very important role in【C11】______the planet's "heat balance". As their name suggests these gases have a similar effect on glass in a greenhouse: They let heat from the sun【C12】______, and keep it in.

The atmosphere is more or less transparent to the【C13】______solar radiation which warms the earth(ground or oceans)on which it falls.【C14】______it has been heated, the earth is warmer than space and gives【C15】______energy in the form. of in visible long-wave infrared radiation. This【C16】______for nighttime cooling. Greenhouse gases【C17】______some of this long-wave radiation, and reradiate it in the lower atmosphere.

The gases【C18】______act rather like a blanket by preventing some infrared radiation from leaving the earth-atmosphere system.【C19】______certain limits, the more greenhouse gases present, the more infrared radiation will become【C20】______, and the higher the surface temperature of the earth.

【C1】

A．current

B．downward

C．upward

D．disturbing

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第5题

非蛋白氮（non-protein nitrogen，NPN)

非蛋白氮(non-protein nitrogen，NPN)

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第6题

氮平衡（nitrogen balance)