Which of the following statement is TRUE?

A: In an efficient market, the only way to earn higher returns is to invest in riskier securities.

B The efficient market hypothesis means that trades can be executed quickly, easily, and inexpensively.

C In a semi-strong efficient market, traders with non-public information would have no advantage over those who had only public information.

D Even if weak form market efficiency is true, it does not mean that studying charts of past prices and searching for repeating pattern is useless.