In actual GMAT you will not find any line number reference questions. Infact there are no line numbers specified on paragraph lines at all. These are only for practice in Books. in actual GMAT the text may be highlighted if any detail question is there and these are among easiest question types because we know where exactly answer lies. We need to comprehend information at the highlighted text and its use in context of overall passage to get to right answer.
I hope this information was helpful.
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