I would state E due to better parallellism.

Fail to DETECT ... INDICATE

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

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

what is teh correct answer and why the rest are wrong

In A, both one and it seem to refer to a condition.
The result is a nonsensical meaning:
Any medical test will sometimes indicate that there is ONE CONDITION when A CONDITION is not.
Eliminate A.

B and D distort the meaning by implying that the purpose of a medical test is to detect a MOMENT IN TIME: WHEN a condition is present.
The purpose of a medical test is to detect the CONDITION itself, not WHEN the condition is present.
Eliminate B and D.

In E, the first it could refer to the presence or to a condition.
Since C avoids this issue and is free of errors, eliminate E.

The correct answer is C.

The OA:
Any medical test will sometimes fail to detect a condition when it is present and indicate that it is present when it is not [present].
Here, each instance of it has the same, clear referent: a condition.
Note the use of ELLIPSIS: the word in brackets is omitted, but its presence is clearly understood.
The ellipsis is made clear by the PARALLEL FORMS: that IT IS PRESENT when IT IS NOT [PRESENT].
Only the OA offers these parallel forms at the end of the sentence.

Thank u for ur reply,
I am not a native speaker, so still cant understand what's the meaning problem with A. What's the problem if both words refer to the word condition?

GMATGuruNY wrote:

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

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

what is teh correct answer and why the rest are wrong

In A, both one and it seem to refer to a condition.
The result is a nonsensical meaning:
Any medical test will sometimes indicate that there is ONE CONDITION when A CONDITION is not.
Eliminate A.

B and D distort the meaning by implying that the purpose of a medical test is to detect a MOMENT IN TIME: WHEN a condition is present.
The purpose of a medical test is to detect the CONDITION itself, not WHEN the condition is present.
Eliminate B and D.

In E, the first it could refer to the presence or to a condition.
Since C avoids this issue and is free of errors, eliminate E.

The correct answer is C.

The OA:
Any medical test will sometimes fail to detect a condition when it is present and indicate that it is present when it is not [present].
Here, each instance of it has the same, clear referent: a condition.
Note the use of ELLIPSIS: the word in brackets is omitted, but its presence is clearly understood.
The ellipsis is made clear by the PARALLEL FORMS: that IT IS PRESENT when IT IS NOT [PRESENT].
Only the OA offers these parallel forms at the end of the sentence.

Hi Mitch,

My query is regarding use of "When".
I know that "when" is used not to indicate a situation but an instance of time or period.
Hence we eliminate option b and d.
But isn't it same in option E -
the presence of a condition when it is there and indicate its presence

Or is it a rule on which the elimination of an option should not solely hing.

Thanks,

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

Hence C !