语法题 og 10 36

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

答案是A
但是为什么native不用复数
还有natives of South America 到底有什么错?
谢谢各位大师了！