Final answer:
The most useful and practical way to minimize air resistance in an experiment on gravity's effects on falling objects is to conduct the experiment in a vacuum.
Step-by-step explanation:
The MOST useful and practical way to minimize air resistance in an experiment concerning gravity's effects on falling objects would be to conduct the experiment in a vacuum (Option C). In a vacuum, there is no air to create air resistance, allowing for a more accurate study of gravity's effects on falling objects. By eliminating air resistance, the falling objects will experience a more consistent and predictable acceleration towards the center of the Earth, regardless of their mass.