题目

Polar bears have patrolled the planet's icy regions for millions of years longer than previously thought — riding out several episodes of global warming in that time. While this suggests their future might not be so bleak, it does not ensure that they will survive the melting occurring in the polar regions today.An international team of researchers has just completed the most comprehensive analysis yet of the polar bear genome (基因组). The team examined DNA from 23 living polar bears and a 110,000-year-old polar bear jawbone. Aided by comparisons with the genomes of brown and black bears, they found that polar bears first emerged as a separate species between four and five million years ago. Previous studies had suggested the species didn't diverge (分化) from brown bears until much later — perhaps just 600,000 years ago.The analysis also showed that polar and brown bears have sometimes interbred (杂交) since their initial divergence and that populations of polar bears have been changing over the past million years in accordance with the climate. Polar bear numbers dropped during warm periods but soared again with prolonged ice ages — most noticeably during a cooling period between 800,000 and 600,000 years ago. The population looks set to fall again as melting pack ice forces polar bears back to the land-based habitats (栖息地) of brown bears, where interbreeding has recently been observed. Should extensive interbreeding occur, both polar and brown bear populations could decline with the emergence of a new hybrid species.The team says that the analysis reveals that polar bear DNA has lost diversity as the population has decreased, drifted apart, and become genetically isolated, suggesting today's bears have less adaptability to environmental change, habitat loss, pollution, and diseases they now face.What does the author say about the future of polar bears?()A They will not survive due to the melting occurring in the polar regions today.B We cannot be sure whether they will survive.C They will certainly survive after patrolling the planet's icy regions for millions of years.D We can help them to ride out the global warming this time again.

Polar bears have patrolled the planet's icy regions for millions of years longer than previously thought — riding out several episodes of global warming in that time. While this suggests their future might not be so bleak, it does not ensure that they will survive the melting occurring in the polar regions today. An international team of researchers has just completed the most comprehensive analysis yet of the polar bear genome (基因组). The team examined DNA from 23 living polar bears and a 110,000-year-old polar bear jawbone. Aided by comparisons with the genomes of brown and black bears, they found that polar bears first emerged as a separate species between four and five million years ago. Previous studies had suggested the species didn't diverge (分化) from brown bears until much later — perhaps just 600,000 years ago. The analysis also showed that polar and brown bears have sometimes interbred (杂交) since their initial divergence and that populations of polar bears have been changing over the past million years in accordance with the climate. Polar bear numbers dropped during warm periods but soared again with prolonged ice ages — most noticeably during a cooling period between 800,000 and 600,000 years ago. The population looks set to fall again as melting pack ice forces polar bears back to the land-based habitats (栖息地) of brown bears, where interbreeding has recently been observed. Should extensive interbreeding occur, both polar and brown bear populations could decline with the emergence of a new hybrid species. The team says that the analysis reveals that polar bear DNA has lost diversity as the population has decreased, drifted apart, and become genetically isolated, suggesting today's bears have less adaptability to environmental change, habitat loss, pollution, and diseases they now face. What does the author say about the future of polar bears?() A They will not survive due to the melting occurring in the polar regions today. B We cannot be sure whether they will survive. C They will certainly survive after patrolling the planet's icy regions for millions of years. D We can help them to ride out the global warming this time again.

题目解答

答案

我们来逐步分析这道题：

题目内容回顾：

文章主要讲述了科学家通过分析北极熊的基因组，发现北极熊作为一个独立物种已经存在了 400万到500万年，远比之前认为的 60万年 更久。这说明它们曾经经历过多次全球变暖，并成功存活下来。然而，文章也指出，这并不意味着它们一定能挺过当前北极地区冰川融化的危机。

文章进一步提到：

  • 北极熊和棕熊之间曾发生过杂交；
  • 北极熊的数量在气候变暖时会减少，在冰川时期会增加；
  • 当前冰川融化导致北极熊回到陆地，与棕熊接触，杂交现象再次出现；
  • 如果大规模杂交发生，可能导致两个物种的数量都下降；
  • 北极熊的基因多样性已经减少，这使得它们更难适应当前的环境变化、栖息地丧失、污染和疾病。

问题：

What does the author say about the future of polar bears?
（作者对北极熊的未来说了什么？）

选项分析：

A. They will not survive due to the melting occurring in the polar regions today.
（由于今天北极地区的冰川融化，它们将无法生存。）
❌ 错误。文章并没有明确说北极熊一定无法生存，只是说它们的未来“并不那么乐观”（not so bleak），但也不保证能生存下来。

B. We cannot be sure whether they will survive.
（我们无法确定它们是否能生存下来。）
✅ 正确。文章明确指出：“it does not ensure that they will survive the melting occurring in the polar regions today.”（这并不保证它们能挺过今天北极地区的冰川融化。）也就是说，作者认为北极熊的未来不确定。

C. They will certainly survive after patrolling the planet's icy regions for millions of years.
（在北极地区游荡了数百万年后，它们肯定会生存下来。）
❌ 错误。虽然北极熊已经存在了数百万年，但文章强调这并不能确保它们能挺过当前的环境危机。

D. We can help them to ride out the global warming this time again.
（我们可以帮助它们再次挺过这次全球变暖。）
❌ 错误。文章没有提到人类可以或正在帮助北极熊应对当前的危机。

正确答案：

$\boxed{B}$

解析

考查要点：本题主要考查学生对文章主旨的理解，特别是作者对北极熊未来命运的判断。需要结合文章中的关键结论，如北极熊的进化历史、基因多样性变化以及当前环境挑战之间的关系。

解题核心思路：

  1. 定位关键句：文章首段明确指出“这并不保证它们能挺过今天北极地区的冰川融化”，这是作者对北极熊未来的核心观点。
  2. 排除干扰项：需注意文章虽提到北极熊曾多次适应气候变化，但强调“不能确保”当前存活，因此排除绝对化的选项（如A、C、D）。
  3. 逻辑推断：结合基因多样性减少、栖息地丧失等不利因素，进一步支持“未来不确定”的结论。

关键信息提取

  1. 北极熊的进化历史：北极熊作为独立物种存在约400-500万年，曾多次经历全球变暖并存活下来。
  2. 当前挑战：
    • 基因多样性减少：适应能力下降。
    • 栖息地变化：冰川融化迫使北极熊与棕熊接触，可能引发杂交，导致种群数量下降。
  3. 作者态度：文章明确指出“不能保证它们能存活”，但未直接否定存活可能。

选项分析

  • A选项：错误。文章未明确断言北极熊“无法存活”，仅指出未来存在不确定性。
  • B选项：正确。直接对应文中“does not ensure they will survive”，强调未来不可预测。
  • C选项：错误。虽北极熊历史悠久，但文章强调“不能确保”当前存活。
  • D选项：错误。文章未提及人类干预的作用，属于过度推断。