Answer:
What instrument can you hear but never see?
No matter how little or how much you use me, you change me every month. What am I?
Often found in doctor's offices and pirate flags
You fill it and it empties, A metaphor for plenty, Depending on what half you see, It's either full or empty
What you do to determine the length of something
What language does a billboard speak?
Easy
Animal
Difficult
Food
Funny
Kids
Logic
What am I?