Question:
Goal: a scale

Which of the following methods is more reasonable for accomplishing this goal?
Answer:
can measure weight accurately

Question:
Goal: How to create an anti-allergen vacuum cleaner.

Which of the following methods is more reasonable for accomplishing this goal?
Answer:
First decide if you want to make a bag, or bag-less model, then decide if you want to make an upright or cannister model, finally consider what type of allergens you wish to block and address those through appropriate filtering devices.

Question:
Goal: how do you reflect something?

Which of the following methods is more reasonable for accomplishing this goal?
Answer:
put a mirror in front of it.