Brief Answer:
Likely due to prolonged exposure of kit to urine

Detailed Answer:
Hi dear, I have reviewed your urine pregnancy kit photograph. It seems to be evaporation line, which forms when the kit is kept for a prolonged time after putting urine sample in it.
Please do tell me the duration after which this line appeared and what is the date of the last menstrual period of the person.
Hope you found the answer helpful. Please do get back with the information, if feasible.
Wishing you good health.
Regards
Dr Deepti Verma

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