B居然多一个a！！

居然暗戳戳加了一个a………………哭辽

D: as the poster above was trying to explain, "work at xxxxx" is not an idiomatic expression here.

even if you don't know this, though, you should still be able to pick (a) over (d), because (a) is more direct and efficient in its language.
i.e., even if (d) were idiomatic (it isn't), it would still be inferior to (a):
works ... at the prevention of X
vs.
prevents X
there's no question which of these has greater economy of expression.

D: as the poster above was trying to explain, "work at xxxxx" is not an idiomatic expression here.

even if you don't know this, though, you should still be able to pick (a) over (d), because (a) is more direct and efficient in its language.
i.e., even if (d) were idiomatic (it isn't), it would still be inferior to (a):
works ... at the prevention of X
vs.
prevents X
there's no question which of these has greater economy of expression.

B: 多了一个a ，会产生是两种drugs的歧义
A：does放在名词后可（preferred）,像B中前置也可。
【copy】如果在平行结构的后半部分，名词后面（注意是后面）跟着修饰成分，则必须！把do / does 放在名词之前
例
than my brother, who has never studied literature, does. --> F
than does my brother, who has never studied literature,. --> T

(A) 正确，aspirin与blood-thinning drug在prevent blood clots上的比较，does指代prevents，补出以 避免歧义。
(B) a commonly used and a more expensive中的第二个冠词a多余，使得句意变化，成为两种drug。
(C) 助动词will应该为does，因为原句用的一般现在时prevents则不是将来时态。
(D) works at prevention of…的表达方式啰嗦；缺少助动词does。
(E) works at preventing…的表达方式啰嗦；which引导定语从句修饰drug啰嗦，不如直接用形容词作定语。

the main problem with option B is the article "a"

aspirin prevents blood clots just as well as does a commonly used and a more expensive blood-thinning drug
the second "a" kind of implies that there are two drugs rather than one.

D, A works as well as B at the prevention of C, B要补出谓语动词，否则会让人误解为 A works at the prevention of C as well as at the prevention of B
E, at preventing blood clots强调在preventing这个过程有效，应该用at the preventing或at the prevention，强调是对prevent的结果有效

well副词，prevent the disease well 很好地预防疾病的发生

E表达啰嗦 work at 和which不优

关于do的位置，Ron解释过：
如果只有一个名词，没有修饰成分，在平行结构的后半句，可以把helping verb（do / does）放在名词的前面或者后面
例
than my brother does. --> correct （preferred）
than does my brother. --> correct
如果在平行结构的后半部分，名词后面（注意是后面）跟着修饰成分，则必须！把do / does 放在名词之前
例
than my brother, who has never studied literature, does. --> F
than does my brother, who has never studied literature,. --> T
此题不受这个规则影响

the main problem with option B is the article "a"

aspirin prevents blood clots just as well as does a commonly used and a more expensive blood-thinning drug
the second "a" kind of implies that there are two drugs rather than one.