Any medical test will sometimes fail to detect a condition when it is

Sorry my answer is wrong. The correct explanation is :-

First, let's think about what the sentence is trying to say without pronouns - it's trying to point out a problem and its obverse: detect a condition when the condition is present vs. indicate that the condition is present when the condition is not present.

A) does a fine job with the first bit (detect a condition when it is present) but messes up the second bit "indicate that there is one when it is not" - indicate there is one what? One condition? It sounds like it's saying something like "one condition exists." The point is to indicate the presence of the condition in a particular circumstance, not its mere existence on the planet.

B) repeats that same error

C) does a fine job with the first bit (detect a condition when it is present) and the second bit (indicate it is present when it is not). Fine.

D) muddies the meaning by moving "when" to the front (B does this too). It sounds like the test just can't detect the timing of the condition, as though, sometimes I have cancer and sometimes I don't and the test can't tell when I do or don't. Really, the test is failing to detect the condition itself, not the timing of the condition. See E for the problem at the end of this choice.

E) "indicate its presence when it is not" is incorrect - that translates as "indicate its presence when it is not presence (last word implied)" which doesn't make any sense. We need to say "indicate that it is present when it is not present (last word implied)." Also "the presence of a condition when it is there" is wordy. "a condition when it is present" is much cleaner.

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