1、so/as只能用于否定句，not so/as=not as/as, as/as可以用在肯定句也可以用在否定句，如：He is not as tall as me.;
not so much/as表示与其说/不如说，如：The distinctions lie not so much in specific skill as in our ability to extend knowledge.
2、last可以跟from/to，可以跟between/and，也可以直接跟时间，如：last (for) three hours
prove，动词。可以是人prove也可以是物prove也可以用被动，如：This proves (that) I was right. 这证明我是对的。；Can this hypothesis be proved？
prove还有是的意思，可以替换成be动词，语意为被发现是，被证明是，如： sth proves dangerous. or sth proves to be dangerous.
hypothesis: this vaccine was the source of the virus found in mesotheliomas decades later.
因此需要选择的选项是支持：（被污染的）疫苗是病毒的来源
E之所以正确，是因为：
在美国，组织中有病毒——疫苗被污染
在芬兰，组织中没病毒——疫苗没被污染
因此芬兰的情况证明了病毒是来源于被污染的疫苗的结论。
at costs介宾作状语修饰utilities obtain power，
utilities obtain power at costs that are higher than costs for smaller plants. ok
E,因为they的存在， that没做成分，不是宾语从句，错误
1、so/as to如此，以至于，语意上等于so/that，如：The girl was so excited as to shout herself hoarse. 那个女孩兴奋得喊哑了嗓子。
as to后接动词，动词的逻辑主语是主句主语；so/that后接句子，有自己的主语
so as to=to，目的是，如my father will go to Beijing so as to see his old friend.
so that=so，因此，或=in order that，以便，为了，如：Bring it nearer so that I may see it better.
2、so/that表如此/以至于，带因果关系，enough/to表足够/而能够
which最好就近修饰，B里which不仅隔了on earth这个地点状语，还隔了the largest lake这个宾语（is表示等于，最大的湖=c，但语意上C是最大的湖，这里最大的湖是一种身份，不是最大的湖覆盖了，是C自己覆盖了），不好！
C，Caspian is the largest lake, covering many areas=Caspian is the largest lake, with that C covers many areas. 伴随状语ok
如果把伴随状语视同带主句主语的独立主格，加上with，并将with sb doing sth视同带定语的介宾结构作状语，则C=Caspian is the largest lake, with Caspian covering many areas，C是最大的湖，伴随着C覆盖了很大的面积，ok
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Wrong: since/because A do sth, consequently B happens, consequently与since/because语意重复。
Right：A do sth, consequently B happens.