Answer:
Who is the most foreign visitor you could imagine?
I run through hills. I veer around mountains. I leap over rivers. And crawl through the forests. Step out your door to find me.
I reach for the sky but clutch to the ground. Sometimes I leave but I am always around.
I am often sold by children entrepreneurs in summer time
Part carbon part water I am poison to the fishes. Many falsely claim my name I am the pause that refreshes.
No matter how little or how much you use me, you change me every month.