Which is true about the M-square measure?

It is the difference between the rate of return of a portfolio with the right amount of leverage to match the standard deviation of a passive index and the rate of return of that passive index.

It is a measure of portfolio excess return divided by its beta.

It is used to measure the portfolio excess return, adjusted for the portfolio delta.

It is a ratio of alpha divided by the standard deviation of the diversifiable risk.

It is a measure of portfolio excess return divided by its standard deviation.