In actual practice, what is one way to find a stocks beta? Group of answer choices a. Find the stock's variance and take the square root of that number. b. Find the stock's variance and regress it onto the market's variance. c. Regress a time series of the stock's returns onto a time series of returns for some market proxy (e.g. the S&P 500 Index). d. Regress a time series of the stock's standard deviations onto a time series of standard deviations for some market proxy (e.g. the S&P 500 Index)