Sentence Correction

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 and indicate its presence

OA: C

I understand the OA but I don't understand the explanation that OG gives for choice A.

It states "The construction there is one leaves it in the final clause without a referent.

Someone please decipher what it means.

"It" normally refers to something.
e.g. Mary likes ice-cream but Steve does not like IT.
In this sentence "it" refers to "ice-cream" so ice-cream is the REFERENT.

The OG explanation states that "it" in the final clause does not represent any noun from the previous clause, which makes the sentence incorrect.

Thanks Kasia for the prompt reply.

But aren't all the 'it' in the sentence referring to 'condition' in choice A.

As per my understand, the two 'it' highlighted in red and the 'one' in green refer to condition. Please correct me here.

Any medical test will sometimes fail to detect a condition when it is present and indicate that there is one when it is not.