The slight failures of memory that many of us attribute to a failing brain are often due to something entirely different:anxiety,sleep problems,depression,even heart disease.The biological nuts and bolts of learning and memory in fact change little over time in healthy people,researcher say.¡°There¡¯s very little cell loss,and structurally all the machinery is there,even very late in life,¡±said a neuroscientist Greg Cole.It¬ðs the cells¬ð speed and ability to send and receive signals that diminish gradually,which is what makes the mind go blank when trying to recall familiar words and names.

    For more than a decade,researchers have known that people who have active,intellectually challenging lives are less likely to develop dementia than those who do not.Part of this difference is attributable to intelligence,some doctors believe:The more you start with,the longer it takes to lose it.And new evidence suggests that the act of using your brain is in itself protective,no matter who you are.

    All of the activities,such as reading newspapers,watching TV,playing games,etc.,can improve people¬ðs scores on standard tests measuring recall of numbers and names,experts say.They also acknowledge,however,that there is a big difference between playing chess with a friend and doing a mental exercise,such as memorizing numbers.One is an organic part of a person¬ðs life,the other a purely intellectual exercise,done in isolation.The first is fun;the second,often,is a tiring task.

31. According to the text,adult persons usually
£ÛA£Ý stress the settlement of bigger problems.
£ÛB£Ý focus their attention on great issues.
£ÛC£Ý overlook the remembrance of trivial things.
£ÛD£Ý suffer memory decline related to age.

32. According to new research,it¬ðs distinct that
£ÛA£Ý our brain cells can be producible.
£ÛB£Ý our memory may be renewable.
£ÛC£Ý most mental illnesses are curable.
£ÛD£Ý brainª²mending methods are available.

33. The phrase ¡°nuts and bolts¡± in Par.3 most probably means
£ÛA£Ý basic structures.
£ÛB£Ý complex tasks.
£ÛC£Ý practical aspects.
£ÛD£Ý working parts.

34. As asserted by researchers,our i
nability to memorize words or names mainly
£ÛA£Ý results from the declining efficiency of brain cells.
£ÛB£Ý results in the brain¬ðs liability to radical interference.
£ÛC£Ý consists of different mental disorders.
£ÛD£Ý consists in various emotional problems.

35. Experts suggest that the best way to avoid memory failures is
£ÛA£Ý to take more dietary supplements.
£ÛB£Ý to keep mental function alive.
£ÛC£Ý to find an intellectual occupation.
£ÛD£Ý to do more intellectual exercises.

Text 4

    Non-indigenous (non-native) species of plants and animals arrive by way of two general types of pathways. First, species having origins outside the United States may enter the country and become established either as free-living populations or under human cultivation¡ªfor example, in agriculture, horticulture, aquaculture, or as pets. Some cultivated species subsequently escape or are released and also become established as free-living populations. Second, species of either U.S. or foreign origin and already within the United States may spread to new locales. Pathways of both types include intentional as well as unintentional species transfers. Rates of species movement driven by human transformations of natural environments as well as by human mobility¡ªthrough commerce, tourism, and travel¡ªgreatly exceed natural rates by comparison. While geographic distributions of species naturally expand or contract over historical time intervals(tens to hundreds of years), species- ranges rarely expand thousands of miles or across physical barriers such as oceans or mountains.