问OG41

41. Under a provision of the Constitution that was never applied. Congress has been required to call a convention for considering possible amendments to the document when formally asked to do it by the legislatures of two-thirds of the states.
(A) was never applied, Congress has been required to call a convention for considering possible amendments to the document when formally asked to do it
(B) was never applied, there has been a requirement that Congress call a convention for consideration of possible amendments to the document when asked to do it formally
(C) was never applied, whereby Congress is required to call a convention for considering possible amendments to the document when asked to do it formally
(D) has never been applied, whereby Congress is required to call a convention to consider possible amendments to the document when formally asked to do so
(E) has never been applied. Congress is required to call a convention to consider possible amendments to the document when formally asked to do so

答案是没有问题的，我的问题是OG的解释中说 A B C D contain tense errors (the use of was never applied with has been required in A) 是什么意思？还有uses of a pronoun it with no noun referent?  it 不能指代amendments 吗？                                   

哦

没有注意词的数 谢谢