比较的题型：1）比两样东西（名词），2）比两个动作（动词）。
这里比较的是两个动作，所以，有一个省略用法 [sub+verb]+modifier，只保留modifier，选C。
如果是比较两个东西, 比如circulation in.... is lower than that in ....，就应该是D。
（newspaper）{had} 《lower circulation》 in the six months than（newspaper）{ had} in a similar period
改写为两个东西比较：the circulation of newspaper in the six months is lower than that in a similar period
In arguing that this decline of feudalism was economically determined, the Marxist asserted that the Black Death was a relatively insignificant factor. 其实还是文章理解不到位；
many schools do not have, or are likely to have=many schools do not have, or many schools are likely to have，that's why not后面跟nor不跟or
nor和or/and一样是连词，that's why D选项后面跟了主语they，有两个独立的句子还是对的，因为nor是连词，且是并列连词！！
FANBOYS：for, and, nor, but, or, yet, so
默念：遇到FANBOYS for and nor but or yet so 的句子，拆开独立的看～ not不要遗漏。
头大，第二次还是错，对A最大的疑问是more than all the North American Great Lakes combined到底是什么成分；
Ron说“more than all the North American Great Lakes combined”作定语修饰“20 percent of the world's fresh water”，整个应该放到which的定语从句里面作为次级修饰语，和“holds … water“一起修饰贝尔加湖；看着还行，因为如果省略了中间的“which holds 20 percent of the world's fresh water”， “more than 五大湖”直接接到“贝尔加湖”后面就毫无意义了。
后面省略了动词do, 如果是👇这样应该就清楚了很多：
Siberia's Lake Baikal, which holds 20 percent of the world's fresh water more than （DO） all the North American Great Lakes combined=>贝加尔湖，它拥有世界上20%的淡水，比北美五大湖（拥有）的总和还要多
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idioms：agree to be/do是错误的