错选A
rate不能用fast修饰，可以说fish are growing fast或者the rate is high。
E选项的with后面的cut不知道动作的发出者是谁。与后面的raising不平行
C选项growing them naturally表示养鱼者自然养鱼的速度，应该是鱼自然生长的速度。illogical

rate不可以是fast，只能是high
前后比较的是一个动作
grow them naturally逻辑上说不通

错选C
grow 而且还是naturally 应该是一个主动的状态

(A) as fast as的前后是一个动作(are growing)和一个名词(growth rate)进行比较,比较概念不对等

C中："growing them naturally" is illogical.
in this construction, "them" (= fish) is the OBJECT of "growing". this implies that someone else must be growing the fish -- which doesn't make sense if we're talking about natural growth.
意思错 C 与自然增长必须是主动，不能是growing them naturally，将原句的意思更改为“供应商养殖鱼类的生长速度和供应商自然养殖鱼类的速度做比较”,不可能是供应商自然增长地养鱼。应该是 鱼自然生长

rate can be high, but cannot be fast.

AB都不是平行结构，growing them naturally不合逻辑，应该是they grow naturally

growing them naturally不合逻辑，应该是they grow naturally

句子结构: To meet…, suppliers are growing fish twice as fast as…
(A) as fast as的前后是一个动作(are growing)和一个名词(growth rate)进行比较,比较概念不对等
(B)比较概念不对等.后一个分句的allotment cut and raising不对等.
(C) 逻辑意思不正确,原句的意思是供应商养殖鱼类的生长速度和鱼类自然生产速度作比较,该选项中growing them和growing fish构成平行,将原句的意思更改为供应商养殖鱼类的生长速度和供应商自然养殖鱼类的速度做比较,
(D) 正确,正确的表现了原句的逻辑意思,既供应商养殖鱼类的生长速度和鱼类自然生产速度作比较
(E) 后一个分句中and raising them没有平行的对象.

先排除结构错的（平行），然后看意思逻辑（C,看起来非常平行，迷惑选项），最后看代词时态（没有错的）

rate can be high, but cannot be fast
且比较前面应该有个rate

"growing them naturally" is illogical.
in this construction, "them" (= fish) is the OBJECT of "growing". this implies that someone else must be growing the fish -- which doesn't make sense if we're talking about natural growth.
意思错 C 与自然增长必须是主动，不能是growing them naturally，不可能是供应商自然增长地养鱼。应该是 鱼自然生长

Allot分配

D选项是否存在代词不明确的问题：
找其他选项有没有用名词代替的split

also:
in general, OBJECTS OF PREPOSITIONS are very rarely the antecedents of pronouns. (i won't say never -- but rarely enough that, if you have to make a random guess, this is probably a pretty good standard by which to make such a guess.)

HOWEVER,
2) if you see an ambiguous pronoun that is NOT replaced by the correct noun in any of the other answer choices, then DON'T eliminate!
for an example, see problem 21 in the blue verbal supplement (in which the correct answer contains a technically ambiguous pronoun).
or see the problem in this thread!

1) if you see an AMBIGUOUS PRONOUN that is REPLACED BY THE CORRECT NOUN in OTHER ANSWER CHOICES, then ELIMINATE the ambiguous pronoun and keep the specific noun.
for an example, see problem 68 in the blue verbal supplement, in which "them" is split against "these companies".

Ron:
C选项：(c) suggests that even natural growth still has to be performed by the suppliers.

D选项是否存在代词不明确的问题：
this is a good point -- the correct answer to this problem, yet again, contains a pronoun that is technically ambiguous.

however, as we've seen again and again and again and again, not all ambiguous pronouns are incorrect!

so here's the simplest way of making the decision:

mark,
rate can be high, cannot be fast

RATE CAN NOT BE FASTER
FISH GROW NATURALLY, NOT SOMEONE GROW FISH NATURALLY

只关注语法了，没关注意思，C的语法应该是没错的吧，但是逻辑意思是错的。

第n次错。。。。。对自己呵呵哒

rate cannot be fast

C 与自然增长必须是主动，不能是growing them naturally，不可能是供应商自然增长地养鱼。