If you live in a region where winter weather is a regular risk, you are likely used to pouring salt on your sidewalks. But how does it work? And how much salt do humans pour onto our planet’s surface? The second question is easier to answer: a lot.
Salt doesn’t directly melt ice, nor does it make snow simply disappear. Instead it makes water less likely to freeze in a phenomenon called freezing point depression. In the case of simple rock salt, which is a rawer, less pure version of table salt, each molecule (分子) splits into smaller elements. Normally, when water freezes into ice, its molecules line up to form a stable, orderly structure. Salt interrupts the process, however, and temperatures must drop lower to overcome that interruption and for freezing to occur.
But if salt needs to interact with liquid water, how does it do anything when temperatures are stubbornly below freezing, and water should already be in the form of ice? That’s where cars help clear their own way by creating friction and, in turn, heat. The friction allows for the ice that has already frozen to melt a little bit, making it unlikely to freeze.
Beyond rock salt’s ability to clear icy streets, it can also be destructive. Chloride ions (氯离子) can cause wear and tear on vehicles and facilities. Increasing chloride densities in North American lakes could begin to upset local ecology and degrade sources of drinking water.
Many local governments are looking for alternatives to rock salt. Other salts such as magnesium chloride and calcium chloride work in the same way as rock salt, and they’re perhaps even more efficient. Some experiments are testing other ice-preventing solutions, including those that contain sugars instead of or in addition to salts. Another approach relies more heavily on sand, which can mechanically make roads safer. All of this experimentation is aimed at ensuring people can travel in any weather condition — a Herculean task when winter brings its worst.
【小题1】What’s the purpose of the first sentence in Paragraph 2?A.To introduce the topic. | B.To give some evidence. |
C.To define the phenomenon. | D.To reveal the misconception. |
A.By lowering the temperature. | B.By melting and splitting itself. |
C.By lining up to form a solid structure. | D.By stopping the formation of the structure. |
A.Concentrations. | B.Weights. | C.Qualities. | D.Salts. |
A.Other salts won’t disturb local ecology. |
B.Efforts are being made to guarantee safe travels. |
C.Many alternatives are available to solve the problem. |
D.Bitter winter make it impossible to secure road safety. |
Why people collect art
Many people throughout history have gone to great lengths to collect art. But what attracts these collectors?
One popular explanation for collecting is that they can have financial(财务的) gain. Some resell works, earning enormous profit.
Collectors are not only interested in creating social links; they are also motivated by the messages they can send once these social networks are created. We all know art is a powerful way for the artist to express thoughts and feelings.
People collect art for various reasons.
A.They gain a lot from artworks from different aspects. |
B.But most collectors think little of profit. |
C.Artworks preserve the qualities of their makers. |
D.No doubt art collection is a hard addiction to overcome. |
E.Some get large tax reductions for donating art to museums. |
F.It also serves as an effective way for collectors to express themselves. |
G.Other art collectors see their collections as having broader power. |
The North Star
Among the pile of stars in the universe, there are a couple that are of great importance to people on Earth. The sun, of course, is one of them. The other is known as Polaris, the North Star.
Before the invention of modern navigation tools, sailors relied on Polaris. From the top of their ships, sailors would look for Polaris to figure out their place at sea. They figured out the angle between the star and the horizon to determine their latitude(纬度). As long as the equations were not wrong, the results were very reliable. Polaris also let sailors determine North, South, East, and West.
To those who sail at night, changeable storms and dark clouds were more than annoying things.
A.It’s not difficult to tell the Polaris apart from the pile of other stars in the universe. |
B.People who are lost can be relieved by gazing up at Polaris. |
C.By knowing directions and their location, sailors could easily steer their ships. |
D.They could destroy entire journeys by blocking the view of Polaris. |
E.It’s certain that the Polaris is part of a constellation(星座), which is not far from it. |
F.It is special because it is the only star that always appears to be in the same place in the sky. |
The Smart Treat Chocolate lovers know that eating chocolate makes them happy. Now it turns out that eating chocolate may also make them smarter. Dr. Bryan Raudenbush recently conducted a study to see how eating chocolate affects people’s brains. The U.S. researchers knew that chocolate contained several stimulants. But he wasn’t sure how those stimulants actually affected chocolate eaters. To find out, Raudenbush had a group of volunteers eat 85 grams of milk chocolate. He asked another group to eat no chocolate at all. After 15 minutes, he tested their memory and their ability to solve problems. The group that ate milk chocolate had higher scores. They were able to remember more words and pictures than the group that did not eat chocolate. Raudenbush concluded that the stimulants in chocolate increased mental alertness. Of course, eating chocolate doesn’t guarantee you’ll pass every test. You’ll still need to study!
【小题1】We can learn from the passage that ________.A.chocolate can help people pass every test |
B.chocolate lovers are smarter than those who don’t love chocolate |
C.chocolate can make people happy and cleverer |
D.chocolate is loved by all the people |
A.Because chocolate contains several stimulants. |
B.Because chocolate made him happy. |
C.To make himself smarter by eating chocolate. |
D.To find out how people’s brains are affected by eating chocolate. |
A.medicine | B.vegetable | C.commercial | D.identification |
A.chocolate is good for health |
B.chocolate tastes better with milk |
C.people’s performance can be improved by eating chocolate |
D.nothing else can be more tasty and effective than chocolate |
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