This stimulus is discussing a study comparing the effects on dust-mite allergy sufferers between the use of mite proof bedding vs. non mite proof bedding. For the mite proof bedding, there was a 69% reduction in allergen in the bedding. In the control (non mite proof), there was no reduction of allergen. However, neither group experienced a reduction in allergy symptoms. This is the conflict/paradox because we clearly expect that a 69% reduction in allergen should have more impact on allergy reduction than no reduction of allergen at all.
For this question type, we need to bring in a new piece of information (from the answer choices), that would allow both items/events to occur. In this case, bedding with reduction of allergen and bedding without reduction of allergen, but neither sees results.
Using answer choice D, this new information says that in order to have a reduction of allergy symptoms, the allergen must be reduced by 90-95%.
Now, we see that neither group satisfied this 90-95% allergen reduction, and this would resolve the conflict and explain why neither group experienced a reduction in symptoms.
I hope this helped, please let me know if you have any other questions.