Run clothes washer only when its full
Answer:
The metric system goes by powers of ten, so it's very easy to measure. That would be the main advantage, measurements of ten. We can also say it's the most used measurement around the world, so all scientists have little to no conversion, but the main answer is probably the first one :)
It is E. because the predators will have slightly more meals with their prey slightly increasing population.
Sapphire.
It is a stone not a metal.