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Suppose that $M$ is an $n\times n$ matrix. Which of the following must be true about the number of singular values of $M$? Select ALL that apply.

$M$ has at most $n$ non-zero singular values.

If $M$ is invertible, then $M$ has exactly $n$ non-zero singular values.

If $M$ has exactly $n$ non-zero singular values, then $M$ is invertible.

$M$ has exactly $n$ non-zero singular values.

None of the above.