What Am I Riddles

Question: i can fill up the entire room and still not take up any space. Who am i?

Question: It takes one word to separate them; otherwise they are inseparable.

What are they?

Question: A cat,mouse,and dog all had an instrument,the dog had a flute,the cat had a trombone and the mouse's instrument bugs the dog.What was the mouse's instrument?

Question: I'm not a pool, a tree, a slave, a website, or a shirt.

What am I?

Question: I travel for miles yet stay where I am. What am I?