1. (2019高一上·上海期中) Choose the one that fits best according to the information given in the passage you have just read.

If you are over 20, look away now. Your cognitive （认知的）performance is probably already on the wane. The speed with which people can process information decreases at a steady rate from as early as their 20s.

A common test of processing speed is the "digit symbol substitution test", in which a range of symbols are paired with a set of numbers in a code. Participants are shown the code, given a row of symbols and then asked to write down the corresponding number in the box below within a set period. There is nothing cognitively challenging about the task: levels of education make no difference to performance. But age does. Speed declines as people get older.

Why this should be is still uncertain, but a range of tentative（尝试性的）explanations has been put forward. One points the finger at myelin, a white, fatty substance that coats axons, which carry signals from one neuron to another. Steady reductions in myelin as people age may be slowing down these connections. Another possibility, says Timothy Salthouse, director of the Cognitive Ageing Laboratory at the University of Virginia, is exhaustion of a chemical called dopamine（多巴胺）.

Fortunately, there is some good news to go with the bad. Psychologists distinguish between "fluid intelligence", which is the ability to solve new problems, and "crystallised intelligence", which roughly equates to an individual's stock of accumulated knowledge. These reserves of knowledge continue to increase with age: people's performance on vocabulary and cognitive decline. In an old but instructive study of typists ranging in age from 19 to 72, older workers typed just as fast as younger ones, even though their tapping speed was slower. They achieved this by looking further ahead in the text, which allowed them to keep going more smoothly.

What does all this mean for a lifetime of continuous learning? It is encouraging so long as people are learning new tricks in familiar fields. "If learning can be absorbed into an existing knowledge base, advantage favours the old," says Mr Salthouse.

1. （1） The phrase "on the wane" (in paragraph 1) is closest in meaning to _______.

   A . declining B . improving C . varying D . maintaining
3. （2） By "age does" (in paragraph 2), the writer means that _______.

   A . the level of a participant's education is related to how old he is B . the older a participant is, the more slowly he writes down the number C . a participant's age affects his ability to figure out what the symbol means D . how much time a participant is given to finish the task depends on his age
5. （3） What can be inferred from the passage?

   A . Dopamine has been proved to be a chemical that affects people's cognitive ability. B . One way to avoid cognitive decline is to have as much experience as possible in life. C . Moving older workers into an entirely new area of knowledge is less likely to go well. D . Crystallised intelligence plays an important role in keeping people alert in new situations.
7. （4） What is the passage mainly about?

   A . Why the brain fails with the age needs to be explored. B . "Digit symbol substitution test" proves to be groundless. C . One's knowledge base matters more than his cognitive ability. D . The brain changes in both good and bad ways as one ages.