My name can have any letter of the alphabet, but I always have 2 X's

Question: My name can have any letter of the alphabet, but I always have 2 X's.

What am I?

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Question: What has a bed that you can't sleep in?

Question: Where do all the letters sleep?

Question: How are doughnuts and golf alike?

Question: What cannot be seen or felt, but can only be broken by voice?