The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.

–Constitution of the United States,
Amendment IX

Which is the best explanation of Amendment IX?

If not clearly stated in the Constitution, a right is not recognized.
To be entitled to a right, a citizen must understand it.
Even if not expressed in the Constitution, a right may still be a right.
Citizens retain all rights that they deem necessary.