An investor starts off owning the market portfolio. She then identifies a stock with positive alpha and decides to add some of it to her portfolio. Adding a small amount of the stock is guaranteed to:

A. Increase the portfolios Sharpe Ratio. B. Decrease the portfolios Sharpe Ratio. C. Increase the portfolios variance. D. Without knowing the correlation between this stock and the market portfolio, we dont know whether it increases the portfolios Sharpe Ratio or not.

Please provide the answer with an explanation