[单项选择]As people age, their cells become less efficient and less able replace damaged components. At the same time their tissues stiffen, For example the lungs and the heart muscle expand less successfully, the blood vessels become increasingly rigid, and the ligaments and tendons tighten.
Few investigators would attribute such diverse effects to a single cause. Nevertheless, researchers have discovered that a process long known to discolor and toughen foods may also contribute to age-related impairment of both cells and tissues. That process is nonenzymatic glycosylation, whereby glucose becomes attached to proteins without the aid of enzymes. When enzymes attach glucose to proteins (enzymatic glycosylation), they do so at a specific site on a specific protein molecule for a specific purpose. In contrast, the nonenzymatic process adds glucose haphazardly to any of several sites along any available peptide chain within a protein molecule.
This nonenzymatic glyeosylation of certain p
A. It paradoxically both helps and hinders the longevity of proteins in the human body.
B. It can be counteracted in part by increased ingestion of glucose-free foods.
C. It is exacerbated by increased enzymatic glycosylation.
D. It probably involves the nonenzymatic glycosylation of proteins.

[单项选择]As people age, their cells become less efficient and less able replace damaged components. At the same time their tissues stiffen, For example the lungs and the heart muscle expand less successfully, the blood vessels become increasingly rigid, and the ligaments and tendons tighten.
Few investigators would attribute such diverse effects to a single cause. Nevertheless, researchers have discovered that a process long known to discolor and toughen foods may also contribute to age-related impairment of both cells and tissues. That process is nonenzymatic glycosylation, whereby glucose becomes attached to proteins without the aid of enzymes. When enzymes attach glucose to proteins (enzymatic glycosylation), they do so at a specific site on a specific protein molecule for a specific purpose. In contrast, the nonenzymatic process adds glucose haphazardly to any of several sites along any available peptide chain within a protein molecule.
This nonenzymatic glyeosylation of certain p
A. It takes place more slowly than glycosylation in the human body.
B. It requires a higher ratio of glucose to protein than glycosylation requires in the human body.
C. It does not require the aid of enzymes to attach glucose to protein.
D. It proceeds more quickly when the food proteins have a molecular structure similar to that of crystallin proteins.

[填空题]To make fears become a less serious problem for children, it is important to help them gain ______.

[填空题]Communication becomes efficient when people understand ______ of cultures.

[填空题]Consumers have become less interested in 3D TV at home, partly because of (have)________ to wear special glasses.

[简答题]Schools have become less important and long-term health care more important as America becomes a society with fewer children and more old people.

[单项选择]Guitar strings often go "dead"—become less responsive and bright in tone—after a few weeks of intense use. A researcher whose son is a classical guitarist hypothesized that dirt and oil, rather than changes in the material properties of the string, were responsible.
Which of the following investigations is most likely to yield significant information that would help to evaluate the researcher’s hypothesis
A. Determining if a metal alloy is used to make the strings used by classical guitarists.
B. Detennining whether classical guitarists make their strings go dead faster than do folk guitarists.
C. Detennining whether identical lengths of string, of the same gauge, go dead at different rates when strung on various brands of guitars.
D. Determining whether a dead string and a new string produce different qualities of sound.
E. (E) Determining whether smearing various substances on new guitar strings causes them to go dead.

[填空题]We become less ______ as the technology gets ever more sophisticated.

[判断题]Women have more fat cells so women have less water.

[单项选择]
Wisdom in old age depends on a fresh supply of new brain cells, a study in mice suggests. When mature mice learn a new task, their newly generated brain cells are three times more active than their old ones, the researchers found. The findings add to a growing body of evidence that the adult brain needs a steady addition of new cells to maintain its mental faculties.
Paul Frankland at the Hospital for Sick Children in Toronto, Ontario, Canada, and colleagues injected a group of mice with a chemical agent that stains only those cells born in the animals’ brains at the time of injection.
One week later, the team taught some of the mice how to navigate through a maze (迷宫), before sacrificing them to analyse the cells in a region of the brain called the hippocampus(海马体),which is key to learning and memory. In stages, the rest of the mice also underwent this paired process of learning and hippocampal exa
A. The mice were given injections for a week.
B. The mice died of the side effects of the injection.
C. The mice were tested and examined at different times.
D. The injection ’affected the mice till they were examine