The zero$-$sum property in CAPM underscores the idea that $...($which of the following options is correct$)$

a$)$ in an efficient and competitive financial market, gains and losses among investors offset each other, ultimately leading to a balance of returns that is consistent with the level of systematic risk borne by each investment

b$)$ in an efficient and competitive financial market, all investors make the same gains, ultimately leading to a balance of returns that is consistent with the level of systematic risk borne by each investment

c$)$ in an efficient and competitive financial market, all stocks yield the same returns, ultimately leading to a balance of returns that is consistent with the level of systematic risk borne by each investment

d$)$ None of the statements is correct