1，我觉得BCD都和原句的意思不同，因为它把原来成为原因的那个三个排比打乱了，所以不对（ancient跑到后面去了），求确认
B、C、D
erosion, prehistoric glacier movement, and volcanic activity
erosion, movement, activity 并列。
而A、E 是
erosion, movement, thrust （名词）并列。
这两种意思上有 轻微的 改变，但应该是允许的。语法上也没错，主要看其他的语法错误吧。
3，题外话：为什么好多题原句是because之后，其他选项里面的since就不选，since不是也有因为的意思么
字典上，since 也有因为的意思 = inasmuch as = because 没有错。
主要A 选项，because of 用错，because of 后面跟 名词短语。
这里because of 后面跟了句。
-- by 会员 abc88 (2012/7/5 13:35:35)
这里的 ancient 和 gold-bearing 都是修饰 riverbeds“ancient” and “gold-bearing” both modify the riverbeds;
the comma is there to keep you from thinking the gold was ancient.
erosion, movement, and riverbeds put gold .....
N1, N2, and N3 VERB OBJECT....
riverbeds
thrust to the surface by volcanic activity划线部分是修饰了riverbeds
since 是解释 前面的一句话~ Prospecting for gold during the California gold rush was a relatively easy task
解释 这个task 为什么 是“容易”的。since 作为连词，引导从句，所以since 后面跟的是 一句完整的句子。没有修饰后面的句子~~后面没句子了。
since N1, N2 and N3 put gold within.....
说错了，riverbeds 才是 第三个名词。
http://www.manhattangmat.com/forums/prospecting-for-gold-during-the-california-gold-rush-t6025-15.html-- by 会员 abc88 (2012/7/5 16:55:22)
(⊙o⊙)，原来如此~~~小哥说的好详细，我一看就懂了~~谢啦~~
as, because, since, for, and in that 的区别
as, because, since, for, and in that
All four of these words can be used to refer to the reason for something. They are not used in the same way.
1. as and since:
As and since are used when the reason is already known to the listener/reader, or when it is not the most important part of the sentence. As - and since - clauses often come at the beginning of sentences. often come at the beginning of sentences.
As it's raining again, we'll have to stay at home.
Since he had not paid his bill, his electricity was cut off.
As - and since - clauses are relatively formal; in an informal style, the same ideas are often expressed with so.
It's raining again, so we'll have to stay at home.
2. because:
Because puts more emphasis on the reason, and most often introduces new information which is not known to the listener/reader.
Because I was ill for six months, I lost my job.
When the reason is the most important part of the sentence, the because - clause usually comes at the end. It can also stand alone. Since and as cannot be used like this.
Why am I leaving? I'm leaving because I'm fed up ! (NOT..... I'm leaving as/since I'm fed up!)
"Why are you laughing? " "Because you look so funny".
A because - clause can be used at the end of a sentence to say how one knows something can be used at the end of a sentence to say how one knows something.
You didn't tell me the truth, because I found the money in your room. ( = .... I know because I found....)
3. for
For introduces new information, but suggests that the reason is given as an afterthought. A for - clause could almost be in brackets. For - clauses never come at the beginning of sentences, and cannot stand alone never come at the beginning of sentences, and cannot stand alone. For, used in this sense, is most common in a formal written style.
I decided to stop and have lunch - for I was feeling hungry.
4. in that
used after a statement to begin to explain in what way it is true
I've been lucky in that I have never had to worry about money.
http://forum.chasedream.com/GMAT_SC/thread-14357-5-1.html
第47楼
-- by 会员 abc88 (2012/7/11 15:12:24)