Answer:
I am a path between high natural masses; remove the first letter to get a path between man-made masses.
I like to twirl my body but keep my head up high. After I go in, everything becomes tight. What am I?
What loses its head in the morning but gets it back at night?
I rise and fall no matter what, only at finals rest do I not budge. What am I?
I repeat only the last word you say. The more I repeat, the softer I got. I cannot be seen but can be heard. What am I?
No matter how little or how much you use me, you change me every month.