The best example of a scientific question that could be used to create an easily reproducible experiment is:
b. Does the mass of a rocket affect the distance it can travel?
This question is specific and allows for a controlled experiment where variables like the mass of the rocket can be systematically changed while measuring the distance it travels, making it repeatable by different scientists.
Option d, "Does sugar or salt have a greater effect on plant growth?" is also a good candidate for reproducibility, but option b provides a clearer and more measurable framework for experimentation.