Respuesta :
C! The amount of bacteria and impurities in water both before and after it passes through his filter!
Explanation:
Although each of these properties of Stuart's filter may be worth testing, the one that will tell him whether his filter can make lake water safe to drink is the amount of bacteria, parasites, and impurities in water both before and after it passes through his filter. Some filters are good at removing impurities, but not bacteria. Other ways of purifying water may kill bacteria but not remove impurities.
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