Answer:
Nothing specific, but more than a few. This many clustered, together will do.
I am the first you ever saw, what greets you every morning and what goes out in the end.
What fastens two people yet touches only one?
What two letters in the alphabet say goodbye?
What is the center of gravity?
It can be cracked, It can be made, It can be told, it can be played. What is it?