List two rules for balancing equations

One answer could be erosion

B? i think so but hope that's right and answers your question

Repeated trials allow you to calculate a mean which can reduce the effect of random errors to make your results more precise.your results will also be reproducible therefore if someone else did the same experiment they'd get the same results which would make your results more reliable.

The object needs to be bigger than you, or (most people would say) you’d be attracting it. no matter how small an object is, if it has mass, it has gravity.