Which one of the following is indicative of a totally efficient stock market?

a$.$ extraordinary returns earned on a routine basis

b$.$ positive net present values over the long$-$term

c$.$ zero net present values for all stocks

d$.$ arbitrage opportunities which develop on a routine basis

e$.$ None of the above. Correct answer $\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$