36. Bufo marinus toads, fierce predators that will eat frogs, lizards, and even small birds, are native to South America but were introduced into Florida during the 1930's in an attempt to control pests in the state's vast sugarcane fields.
A. are native to South America but were introduced into Florida during the 1930's in an attempt to control
B. are native in South America but were introduced into Florida during the 1930's as attempts to control
C. are natives of South America but were introduced into Florida during the 1930's in an attempt at controlling
D. had been native to South America but were introduced to Florida during the 1930's as an attempt at controlling
E. had been natives of South America but were introduced to Florida during the 1930's as attempts at controlling
 
1.时态 (一级排除D，E )
 表示事实和持续存在的 用 一般现在式 ； 过去完成式 有表示过去存在但是过去已经结束的状态In D and E, had been inaccurately implies that the toads are no longer native, or indigenous, to South America,

2.句子逻辑意思 (二级排除B )
Both as attempts in B and E and as an attempt in D are wrong because the attempt consists not of the toads themselves, but of their introduction into the environment. The correct phrase, in an attempt, should be completed by an infinitive (here, to control), as in A.(重要，体会如何用词，蟾蜍自己本身不是一个attempt) as sth  表示作为, 那么作为一定有个东东是”作为”的主语
as attempts / in an attempt  A as B , A 和 B 对等 此处 toads 不可能和 attempts 对等。 In attempt to 在。。。这样的一个动作中。
 
3.表示目的 (三级排除C )
表示目的用不定式比较好

4.词法： 
A. were introduced into Floridaè表示介绍到……地方 ；introduced to Florida is unidiomatic. è表示介绍给…知道

B. native to / native of / native in  用 to 合理，

C. as attempts / in an attempt  A as B , A 和 B 对等 此处 toads 不可能和 attempts 对等。 In attempt to 在。。。这样的一个动作中。