2023年6月英语四级仔细阅读真题及答案解析
　　Section C
　　Passage One
　　Questions 46 to 50 are based on the following passage.
　　Declining mental function is often seen as a problem of old age，but certain aspects of brain function actually begin their decline in young adulthood, a new study suggests.
　　The study, which followed more than 2,000 healthy adults between the ages of 18 and 60, found that certain mental functions—including measures of abstract reasoning, mental speed and puzzle-solving—started to dull as  ...