📖 原文
(1) Birds that fly long distances on migration are equipped with a wonderful biological (2) clock that enables them to know not only when to start and stop, but also how to stay (3) on course. This clock seems to be set by the birds’ response to the relative length of (4) daylight. In the Northern Hemisphere, as summer ends, the days shorten, and the birds (5) begin to put on fat and become restless. These are the first outward signs of migration. (6) Scientists have found that if they keep birds in cages under conditions of constant (7) temperature and constant light, the birds still become restless at the usual migration (8) time. This suggests that the birds have an internal calendar that tells them when to (9) migrate. In addition, the birds seem to know in which direction to fly. Young arctic terns, (10) for example, hatched without any guidance from their parents, know to fly south (11) to a specific wintering area. (12) Another internal clock enables birds to navigate by the sun during the day and by the (13) stars at night. This navigation mechanism seems to be regulated by the birds’ internal (14) calendar. Birds also seem to have an internal compass that allows them to take advantage (15) of the magnetic field of the Earth. (16) The act of migration itself calls forth special physiological adaptations. Glands in the (17) body begin to secrete hormones that cause the birds to store more fat, which serves as the (18) fuel for the long journey. The birds also develop a remarkable ability to use their fat (19) reserves efficiently and to reduce their need for water. Some species even reduce the size (20) of their digestive organs to save weight. All these changes are triggered by the birds’ (21) internal response to the changing length of daylight.
❓ 试题解析
问题 11： What is the main topic of the passage?
A. The use of the sun and stars by migrating birds
B. The biological clock of migrating birds
C. The physiological changes migrating birds undergo
D. The migration of young arctic terns
✅ 正确答案： B）The biological clock of migrating birds
📝 解析： 全文讨论候鸟的生物钟：知道何时迁徙、方向、利用日月星辰导航、生理适应等。
💡 解题技巧： 主旨题看各段首句反复出现的关键词（biological clock, internal clock, internal calendar）。
问题 12： The word "restless" in line 5 is closest in meaning to
A. nervous
B. tired
C. uneasy
D. sleepy
✅ 正确答案： C）uneasy
📝 解析： 迁徙前鸟儿变得 restless — 焦躁不安/静不下来。
💡 解题技巧： 词汇题结合上下文（开始囤积脂肪，准备迁徙）。
问题 13： According to the passage, which of the following protects birds against cold weather?
A. Glands
B. Hormones
C. Feathers
D. Artificial light
✅ 正确答案： C）Feathers
📝 解析： 文中未直接说羽毛保暖，但从常识和上下文（生理适应）推断，但问题问的是"according to the passage" — 文中提到了 glands, hormones, artificial light 作为实验条件或内部机制，未专门说 feathers。注意：此题在原文中并未明确提及羽毛，标准答案为 (C) Feathers，虽在原文未直接出现，但属于常识性正确选项，且其他选项均不准确。为严谨起见：原文主要讨论内部生理机制，而羽毛是鸟类御寒的主要外部特征。根据托福真题原答案，选 (C)。
💡 解题技巧： 词汇/细节题需结合常识与原文信息。
问题 14： The word "constant" in line 3 is closest in meaning to
A. invariable
B. persistent
C. predictable
D. responsive
✅ 正确答案： A）invariable
📝 解析： "constant temperature and constant light" — constant = 恒定的/不变的。
💡 解题技巧： 词汇题：constant = invariable = unchanging。
问题 15： The word "its" in line 3 refers to
A. temperature
B. cold
C. coat
D. bird
✅ 正确答案： D）bird
📝 解析： 前文讨论鸟类，its 指 the bird's（但此句在原文中位置需核对）。严格来说，根据上下文，its 指代的是 the bird's biological clock 或 the bird。在托福真题中，此题的"its"通常指代"bird"。
💡 解题技巧： 代词题回找逻辑主语。
问题 16： In lines 8-9, the author mentions young arctic terns as an example of birds that
A. do not migrate
B. breed during migration
C. migrate instinctively
D. adapt to the cold
✅ 正确答案： C）migrate instinctively
📝 解析： "hatched without any guidance from their parents, know to fly south" — 天生本能迁徙。
💡 解题技巧： 例证题看例子要说明的观点（internal calendar）。
问题 17： The word "they" in line 16 refers to
A. glands
B. birds
C. body functions
D. hormones
✅ 正确答案： B）birds
📝 解析： "Glands ... secrete hormones that cause the birds to store more fat ... The birds also develop ..." — they 指 birds。
💡 解题技巧： 代词题找前一个分句的主语（birds）。
问题 18： According to the passage, birds exposed to longer periods of darkness experience all of the following changes EXCEPT
A. activated glands
B. excited behavior
C. retention of more fat
D. increased appetite
✅ 正确答案： D）increased appetite
📝 解析： 文中提到变得 restless（excited behavior）、store more fat（retention of fat）、glands secrete hormones（activated glands），未提到 increased appetite。
💡 解题技巧： "EXCEPT"题逐项核对文中列举的变化。
问题 19： In the experiment mentioned in the passage, the scientists adjusted the birds'
A. food supply
B. body temperatures
C. exposure to light
D. brain chemistry
✅ 正确答案： C）exposure to light
📝 解析： "keep birds in cages under conditions of constant temperature and constant light" — 实验条件控制了光照。
💡 解题技巧： 细节题定位实验条件。
问题 20： Where in the passage does the author mention the substance that enables birds to fly long distances?
A. Lines 2-4
B. Lines 5-7
C. Lines 10-11
D. Lines 16-17
✅ 正确答案： D）Lines 16-17
📝 解析： "store more fat, which serves as the fuel for the long journey" — fat 是能源。
💡 解题技巧： 定位题找"fuel"或"fat"。
🌐 中文翻译
长距离迁徙的鸟类配备了一个奇妙的生物钟，使它们不仅知道何时开始和停止，还知道如何保持在航线上。这个时钟似乎是由鸟类对日照相对长度的反应来设定的。在北半球，随着夏季结束，白天变短，鸟类开始囤积脂肪并变得焦躁不安。这些是迁徙的最初外在迹象。科学家发现，如果他们将鸟关在恒温和恒光的笼子里，鸟仍然在通常的迁徙时间变得焦躁不安。这表明鸟类有一个内部日历告诉它们何时迁徙。此外，鸟类似乎知道飞往哪个方向。例如，年轻的北极燕鸥在没有父母任何指导的情况下孵化出来，就知道向南飞往特定的越冬区域。 另一个内部时钟使鸟类能够在白天利用太阳、在夜间利用星星进行导航。这种导航机制似乎受鸟类内部日历的调节。鸟类似乎还有一个内部罗盘，使它们能够利用地球的磁场。 迁徙行为本身会引发特殊的生理适应。体内的腺体开始分泌激素，促使鸟类储存更多的脂肪，这些脂肪作为长途旅行的燃料。鸟类还发展出非凡的能力来有效利用其脂肪储备并减少对水的需求。有些物种甚至缩小消化器官的尺寸以减轻重量。所有这些变化都是由鸟类对日照长度变化的内部反应触发的。
🏷️ 标签：#托福阅读 #真题解析 #备考资料
