Which of the statements about investment risk is not correct?

Select one:

a.A sudden decrease in the share price due to the exposure of a company's financial scandal is an example of unsystematic risk.

b.Diversification helps reduce the idiosyncratic risk.

c.The market portfolio is fully diversified and thus has no risk.

d.By putting shares into a portfolio, one share's increase in the return can be offset by the decrease in another share's return, thus reducing the volatility in the aggregate portfolio return.