巨龟乔纳森：探秘长寿密码
Jonathan is a giant tortoise that lives on the island of St. Helena in the South Atlantic Ocean. At about 194 years old, he is believed to be the oldest living land animal in the world. Jonathan belongs to a species called the Aldabra giant tortoise, which is native to the Seychelles islands in the Indian Ocean. Giant tortoises are famous for their long lives, and many of them live for more than a hundred years. But even among them, Jonathan is truly unusual.
Why do giant tortoises live so long? Scientists have long believed that the answer lies in their slow pace of life, even at the level of cells. Compared with humans, their metabolic rate (the speed at which the body works) is much lower. As a result, fewer chemical reactions happen inside their cells, and the cells and DNA suffer less damage. This idea sounds reasonable, but until recently nobody had tested it with Jonathan’s own genes.
In a new study, scientists examined Jonathan’s genome, the complete set of his DNA, and the switches that turn genes on and off. They found 287 gene changes, or variants, linked to protecting the animal from the cell damage that comes with age. In particular, he carries genes that are especially good at repairing DNA and reducing inflammation (the body’s response to harm), two key processes that slow down aging. The most surprising result is that Jonathan can still express the right genes at the right levels even at his great age, but this ability usually deteriorates much earlier in most other animals, including humans.
Scientists still do not fully understand why some animals live so much longer than others. However, the study of Jonathan may offer clues. If researchers can learn how tortoises keep their cells healthy for so long, the findings might one day help develop treatments that slow age-related decline in human cells. As one scientist put it, such knowledge would be a major step forward in our understanding of aging and human health.
1.1. Why is Jonathan unusual even among giant tortoises?
A He lives longer than other animals.
B He is far older than most tortoises.
C He belongs to a rare species.
D He was born in the Seychelles.
解析：选B。B 细节理解题。根据第一段“At about 194 years old, he is believed to be the oldest living land animal in the world.”与“many of them live for more than a hundred years. But even among them, Jonathan is truly unusual.”可知：多数巨龟活过百岁，而Jonathan已近两百岁，在同类中格外不寻常，B正是把这两处合起来说的一句话。A把原文“the oldest living land animal”（最年长的陆地动物）扩大成“比其他动物都长寿”，范围被放大，文中没有这个意思；C “属于稀有物种”，文中只说他属于Aldabra巨龟这一物种，从未说它稀有；D把“which is native to the Seychelles islands”（物种原产于塞舌尔群岛）挪到他本人身上——那是物种来源，他现在住在St. Helena。故选B。
2.2. What did scientists believe led to giant tortoises’ long life before the new study?
A Few natural enemies.
B Better DNA repair.
C Slow cell activity.
D Strong gene control.
解析：选C。C 细节理解题。第二段指出，科学家长期认为巨龟长寿在于“the answer lies in their slow pace of life, even at the level of cells.”，且“their metabolic rate... is much lower”，导致“fewer chemical reactions happen inside their cells”。可知，过去的解释是它们身体运转慢、细胞内反应少、细胞与DNA受损更轻，C“Slow cell activity”概括的正是这条旧观点。B、D是第三段新研究的发现，不符合“before the new study”；A文中未提。故选C。
3.3. What does the underlined word “deteriorates” probably mean?
A Improves gradually.
B Becomes worse.
C Remains stable.
D Occurs earlier.
解析：选B。B 词义猜测题。根据第三段的“Jonathan can still express the right genes at the right levels even at his great age, but this ability usually deteriorates much earlier in most other animals, including humans.”可知，Jonathan在高龄时仍能正常表达基因，而大多数其他动物包括人类的这种能力通常会更早“变差、衰退”，前后形成对比，因此deteriorates最接近“Becomes worse”，选B。A项“逐渐改善”与对比逻辑相反；C项“保持稳定”不符合“usually... much earlier”的转折含义；D项“发生得更早”是对much earlier的误解，不是deteriorates本身的意思。故选B。
4.4. What does the author mainly intend to tell us?
A Giant tortoises are better protected than others.
B Scientists know the secret of living forever.
C Jonathan holds the record for long life.
D Research on Jonathan may benefit humans.
解析：选D。D 写作意图题。全文从乔纳森的高龄写起，先讲长寿的旧解释，再讲新研究发现的基因线索，最后落到“the findings might one day help develop treatments that slow age-related decline in human cells”与“our understanding of aging and human health”——作者写这些，是想说明这项研究对人类健康可能的意义，D“Research on Jonathan may benefit humans.”正是这个落点。A“Giant tortoises are better protected than others.”讲的是保护问题，全文没有涉及；B“Scientists know the secret of living forever.”说得太满，作者自己还留有余地——“Scientists still do not fully understand”、“may offer clues”；C“Jonathan holds the record for long life.”只是第一段的一个事实，撑不起全文。故选D。