og12 verbal Q80关于it的指代问题

xiaoyongnao

80. Any medical test will sometimes fail to detect a_condition when it is present and indicate that there is one when it is not.
(A) a condition when it is present and indicate that there is one
(B) when a condition is present and indicate that there is one
(C) a condition when it is present and indicate that it is present
(D) when a condition is present and indicate its presence
(E) the presence of a condition when it is there andindicate its presence
这题答案选C没有问题，可是A为什么不对呢OG的解释是There is one leaves  it in the final clause without a referent.为什么C的It没有问题，A的it就不行呢？

bodkicker

我觉得
a 选项 it 的指代 和 there is one 中 one 的指代是同一个事物 a condition
因此 one 完全可以换成 it

如果是one 的话 会给人误解  会觉得 和 it 的指代对象 是不同的

如果是不同的话 前面 就没有 可指代的对象了~

xiaoyongnao

嗯嗯有道理，哈哈  谢谢