What is something interesting you learned about the xylphone/marimba

What is placed under the key to help amplify the sound?
What material are the keys of this marimba made from
How long is a full sized marimba?
Draw a Xylophone!
When did the first instruments related to the xylophone appear in eastern Asia?
What did all early xylphones have in common?
What were used as early resonators
Which is NOT a variation of the xylophone?
Albert Roth's two-rowed xylophone introduced what?