Answer:
People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?
What can fill a room but takes up no space?
I help boats park
I am there when you sit, but gone when you stand. What am I?
A thousand wheels, but move I do not. Call me what I am, call me a lot. What am I?
What is always coming but never arrives?