The growth exceeds that which (growth) had been for 10,000 years.
语法难点：宾语that指代growth，其身后的which had been for 10,000 years是that的定语从句，先行词做主语。
主干的中文为：
增长超过了增长，增长是为了10000年的。
增长不能“为了10000年”，10000年应该是增长持续的时间。
综上，答案为A。
as…as…结构和more than原理上是完全一样的，把第二个as当成than即可。例如：
Recent research indicates that two popular arthritis drugs are possibly not as safe as they initially believed.
(A) that two popular arthritis drugs are possibly not as safe as they initially believed
(B) that two popular arthritis drugs may not be as safe as they were initially believed to be
(C) two popular arthritis drugs to possibly not be as safe as it was initially believed
抽取选项A主干：
research indicates that drugs are possibly not as safe as they believed
语法难点：语境中只有drugs是复数，所以代名词they只能指代它。
主干的中文为：
研究揭示药是安全的（相对于：药相信）
在逻辑上，药不能主动发出“相信”这个动作。只有“人”可以。排除选项A。
抽取选项B主干：
research indicates that drugs may not be as safe as they were believed to be
主干的中文为：
研究揭示药是安全的（相对于：药被认为的）
逻辑准确，保留。
抽取选项C主干：
research indicates drugs to possibly not be as safe as it was believed
主干的中文为：
研究揭示药
本选项主句主干的宾语是“药”。基于看大不看小规则，可以直接排除本选项，因为研究不可能揭示“药”。
综上，答案为B。
当然，还有些考题看似是比较，实则纯粹是来送分的，把主干抽清楚即可从容判断。例如：
Several studies have found that the coronary patients who exercise most actively have half or less than half the chance of dying of a heart attack as those who are sedentary.
(A) have half or less than half the chance of dying of a heart attack as those who are sedentary
(B) have half the chance, or less, of dying of a heart attack than those who are sedentary do
(C) have half the chance that they will die of a heart attack, or less, than those who are sedentary do
(D) are at least fifty percent less likely to die of a heart attack as those who are sedentary
(E) are at least fifty percent less likely than those who are sedentary to die of a heart attack
同样地，这道题乍看之下是比较题，但其实只看到宾语从句的主干即可。
选项ABC宾语从句的主干为：
patients have chance.
选项DE宾语从句的主干为（类似于be able to/be likely to/be capable of都可以算作助动词，不是核心动词）：
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这是困扰很多考生甚至包括GMATla学员的问题。
先说结论，答案是“无需考虑所谓比较，直接看清楚每个选项的字面意即可”。因为绝大部分的比较题，要么足够直观，很容易排除掉比较对象错误的，要么就是直接通过成分差异直接判断对错而无需使用“比较”的。
首先考虑比较对象严重错误的。这一点被归类为“刚性语法错误”。例如：
Right：I am taller than you.
Wrong：I am taller than the earth.
但在实际考题中，往往会涉及到一些省略的概念，让人十分头疼。请注意，这些省略，任谁也无法搞清楚是否需要省以及能省，作为考生，我们没有必要去研究这些复杂的省略规则，只需按照比较前后的成分以字面上最合理的意思读清楚，从语法上直接排除那些造成比较对象严重不对等的选项即可。例如：
As Charles Darwin observed, natural selection operates whenever individuals of one genetic composition are better at reproducing than that of others.
(A) that of others
(B) another
(C) those of another
本题最合理的比较对象是基因组成的个体。请注意，“基因组成”本身是不能“繁殖（reproducing）”的，只有基因形成个体后才能繁殖。因此，应该用those指代 individuals，用another对应one genetic composition，答案为C。选项A中的that无指代对象；选项B中的another对应one genetic composition，不能用个体和基因组成比较。
接下来考虑最常见的比较情况。先看一道例题：
Since 1990 the global economy has grown more than it did during the 10,000 years from the beginning of agriculture to 1950.
(A) Since 1990 the global economy has grown more than it did during the 10,000 years from the beginning of agriculture
(B) Since 1990 the growth of the global economy has been more than that during 10,000 years, from when agriculture began
(C) The growth of the global economy since 1990 exceeds that which had been for 10,000 years from the beginning of agriculture
初看例题，很容易确定本题在考“比较”，然后就乱了，各种能省不能省就开始了。这个方式是错的。正确的方法是：
以more than中的than为分界线（可以把than看成一个普通的连词），前后当作两个独立的句子，分别划分清楚成分并且把意思看懂。than身前出现过的内容在身后均可以省掉。
抽取选项A主干：
economy has grown more than it did
主干的中文为： 经济增长 超过 经济增长。
逻辑正确，保留。
抽取选项B主干：
the growth has been more than that
主干的中文为：
增长是超过增长的。
本选项较难判断，看似语意问题也不大。容易发现，本选项和选项A在整个主句的句型上完全不同。类似这样的情况，我们必须借助语境中的状语。句首的Since 1990是状语，在选项A中修饰动作grow；选项B中，其修饰系动词has been。逻辑上来说，一定是“增长”自从1990年开始，而不是“是”自从1990年开始（原则上，无论任何时刻，自从1990年开始的增长都大于过去10000年的增长）。排除选项B。
抽取选项C主干：
The growth exceeds that which (growth) had been for 10,000 years.
语法难点：宾语that指代growth，其身后的which had been for 10,000 years是that的定语从句，先行词做主语。
主干的中文为：
增长超过了增长，增长是为了10000年的。
增长不能“为了10000年”，10000年应该是增长持续的时间。
综上，答案为A。
as…as…结构和more than原理上是完全一样的，把第二个as当成than即可。例如：
Recent research indicates that two popular arthritis drugs are possibly not as safe as they initially believed.
(A) that two popular arthritis drugs are possibly not as safe as they initially believed
(B) that two popular arthritis drugs may not be as safe as they were initially believed to be
(C) two popular arthritis drugs to possibly not be as safe as it was initially believed
抽取选项A主干：
research indicates that drugs are possibly not as safe as they believed
语法难点：语境中只有drugs是复数，所以代名词they只能指代它。
主干的中文为：
研究揭示药是安全的（相对于：药相信）
在逻辑上，药不能主动发出“相信”这个动作。只有“人”可以。排除选项A。
抽取选项B主干：
research indicates that drugs may not be as safe as they were believed to be
主干的中文为：
研究揭示药是安全的（相对于：药被认为的）
逻辑准确，保留。
抽取选项C主干：
research indicates drugs to possibly not be as safe as it was believed
主干的中文为：
研究揭示药
本选项主句主干的宾语是“药”。基于看大不看小规则，可以直接排除本选项，因为研究不可能揭示“药”。
综上，答案为B。
当然，还有些考题看似是比较，实则纯粹是来送分的，把主干抽清楚即可从容判断。例如：
Several studies have found that the coronary patients who exercise most actively have half or less than half the chance of dying of a heart attack as those who are sedentary.
(A) have half or less than half the chance of dying of a heart attack as those who are sedentary
(B) have half the chance, or less, of dying of a heart attack than those who are sedentary do
(C) have half the chance that they will die of a heart attack, or less, than those who are sedentary do
(D) are at least fifty percent less likely to die of a heart attack as those who are sedentary
(E) are at least fifty percent less likely than those who are sedentary to die of a heart attack
同样地，这道题乍看之下是比较题，但其实只看到宾语从句的主干即可。
选项ABC宾语从句的主干为：
patients have chance.
选项DE宾语从句的主干为（类似于be able to/be likely to/be capable of都可以算作助动词，不是核心动词）：
patients die of a heart attack.
显然，常理上，研究揭示的应该是“病人会死于心脏病”而不是“病人有机会”。通过more必须加than不能加as可以排出选项D，答案为选项E。
综上，比较题其实非常简单。以than为分界，把前后两个句子按照成分读清楚即可有效解除答案。