Biologists have long debated about whether egg production in birds is biologically highly costly, some theorizing that egg production is energetically or nutritionally demanding. Lack, however, suggested that clutch size—the number of eggs a bird lays per breeding cycle—is far below the potential limit of egg production. He suggested that clutch size had instead evolved in relation to the number of young that the parents could successfully rear. Subsequently, most studies focused on limitations operating during chick rearing, particularly among altricial species (species in which the parents feed their young in the nest). Lack later recognized that in precocial species (species in which young feed themselves), clutch size might be explained by different factors—the availability of food for egg-laying females, for example.
文章解析
第一句话：
Biologists have long debated about whether egg production in birds is biologically highly costly, some theorizing that egg production is energetically or nutritionally demanding.
白话版讲解：
生物学家们一直在争辩一个问题。从生物学的角度看，下蛋这件事本身对下蛋的鸟来说，是不是一件很耗费体能和营养的事？一些生物学家认为，是。（潜台词，另一些生物学家认为，不是。）
第二句话：
Lack, however, suggested that clutch size—the number of eggs a bird lays per breeding cycle—is far below the potential limit of egg production.
白话版讲解：
However，有一个名字叫Lack的生物学家，暗示说鸟每下一波蛋的蛋的个数，远远低于（没达到）鸟的能力的上限。
第三句话：
He suggested that clutch size had instead evolved in relation to the number of young that the parents could successfully rear.
白话版讲解：
Lack暗示，鸟每下一波蛋下几只，不是由鸟下蛋的能力决定，而是由蛋下出来以后，鸟爸爸鸟妈妈能成功养大几只小鸟来决定的。
Subsequently, most studies focused on limitations operating during chick rearing, particularly among altricial species (species in which the parents feed their young in the nest).
白话版讲解：
（Lack提出以上理论以后，大部分生物学家觉得有道理，就相信他了）。所以此后的大部分研究就主要以鸟蛋孵化以后鸟爸爸鸟妈妈抚养雏鸟那一阶段起作用（operating）的一些限制条件为研究对象了。（而不是以鸟妈妈怀孕时起作用的一些限制条件为研究对象）。对altricial这一类鸟尤其是如此。
第五句话：
Lack later recognized that in precocial species (species in which young feed themselves), clutch size might be explained by different factors—the availability of food for egg-laying females, for example.
1. The passage suggests that biologists who say egg production in birds is biologically highly costly would agree that clutch size is determined primarily by
A. the nutritional and energy demands of egg production
B. the number of young that the parents can rear successfully
C. reproductive limitations operating during chick rearing
D. the availability of food for newly hatched chicks
E. the differences between altricial and precocial species
白话版讲解：
根据文章，altricial和precocial 两类鸟的区别体现在小鸟需不要鸟爸爸鸟妈妈喂吃的，那是鸟蛋孵化以后的事。B、C、D讲的也都是鸟蛋孵化以后的事， 第一种理论讲的是雌鸟怀孕时期的事（怀孕时营养够不够）。这道题问的是第一种理论。所以A选项正确。
Consider each of the choices separately and select all that apply.
2. The passage suggests that Lack would agree with which of the following statements about factors affecting clutch size in birds?
A. In altricial species, clutch size is determined primarily by factors operating after eggs are laid.
B. In precocial species, clutch size is determined primarily by factors operating after eggs are laid.
C. In many bird species, clutch size generally remains well below the potential limit of egg production.
