Which of the following statements about diversification is correct?

a$.$ A stock with a beta of $-1\mathrm{.}0$ has maximum nondiversifiable risk.

b$.$ Portfolio diversification reduces the variability of returns on an individual stock.

c$.$ When the company specific risk has been diversified, the inherent risk that remains is the market risk, which is constant for all secur

d$.$ The systematic risk of a stock with a beta of zero is equal to the market

e$.$ When two perfectly positively correlated stocks with the same risk are combined, the portfolio risk is equal to the risk associated wit