Which of the following statements is most CORRECT, assuming positive risk-free rate and market risk premium?

a) If the risk-free rate increases, and is the only factor affecting stock's return that changes, a stock with bigger beta will have a greater increase in its required return.

b) If the risk-free rate increases, and it the only factor affecting stock's return that changes, a stock with bigger beta will have a greater decrease in its required return.

c) Only two stocks whose coefficient correlation of returns are positive will enjoy diversification benefits.

d) Other things held constant, when market risk premium increases, a stock with bigger positive beta will experience a greater increase in its required rate of return.

e) When market risk premium increases, a stock with positive beta will not experience a fall in price when the stock index (proxy for market portfolio) falls as realised return cannot be negative.