Normally, the constantly changing levels of an animal's activity——sleeping, feeding,moving, reproducing, metabolizing, and producing enzymes and hormones, for example——are well coordinated with environmental rhythms, but the key question is whether the animal's schedule is driven by external cues, such as sunrise or sunset, or is instead dependent somehow on internal timers that themselves generate the observed biological rhythms. (TPO13, 61)

metabolize /mɪ'tæbəlaɪz/ v. 新陈代谢

enzyme /'enzaɪm/ n.酵托福考试带什么

hormone /'hɔːməʊn/ n. 荷尔蒙，激素

rhythm /'rɪð(ə)m/ n.节奏;节律，循环

internal /ɪn'tɜːn(ə)l/ adj.内在的，内部的

我是分界线，大家先自己一遍速读哦。

Normally, the constantly changing levels of an animal's activity(——sleeping, feeding, moving,reproducing, metabolizing, and producing enzymes and hormones, for example——)are well coordinated with environmental rhythms, but the key question is whether the animal's schedule is driven by external cues, such as sunrise or sunset, or is instead dependent somehow on internal timers (that themselves generate the observed biological rhythms). (TPO13, 61)

长难句分析：

这个句子主干部分:

Normally, the constantly changing levels of an animal's activity are well coordinated with environmental rhythms, but the key question is whether the animal's schedule is driven by external cues, such as sunrise or sunset, or is insteaddependent somehow on internal timers.

大家要在读的时候要注意忽略那些细节，尤其是破折号后面的。

比较难理解的是the key question is whether the animal's schedule is driven by external cues, such as sunrise or sunset, or is instead dependent somehow on internal timers.

这里就是A or B的结构：

A= isdriven by external cues, such as sunrise or sunset

or

B= isinstead dependent somehow on internal timers

中文：关键问题是，动物的作息是否是由外界条件比如日出日落驱使，或者相反，是以某种方式依赖于。

修饰一：(——sleeping, feeding, moving,reproducing, metabolizing, and producing enzymes and hormones, for example——)，破折号，解释说明

中文：例如，睡觉、喂食、活动、繁殖、新陈代谢以及产生酶与荷尔蒙

修饰二：(that themselves generate the observed biological rhythms) ，从句，修饰internal timers

中文：自身产生并遵循的生物循环

参考翻译：

一般来说，动物活动的不断变化的程度——例如，睡觉、喂食、活动、繁殖、新陈代谢以及产生酶与荷尔蒙——与环境的循环十分同步，但关键问题是，动物的作息是否是由外界条件比如日出日落驱使，或者相反，是以某种方式依赖于自身产生并遵循的生物循环。

这个句子的主要修饰成分就是从句，大家务必想清楚，每一个修饰成分修饰的是什么，才能看清楚这个句子的结构。