Which of the following will always lower a portfolio's beta?

I. Diversify among different types of securities and across industry and geographic lines.

II$.$ Add investments with low betas to the portfolio.

III. Hold more cash or Treasury Bills in the portfolio.

IV$.$ Reduoe the percentage of the portfolio invested in high beta securities$.$

I, II and IV only

II$,$ III and IV only

I, II and III only

I, II$,$ III and IV