Given a text T, and several options, according to the question posed in the text T to choose the most appropriate option from the options as the answer, please directly output the most appropriate option, do not need to output the explanation.

With respect to rational and irrational investment decisions, the efficient market hypothesis requires:
Option A:only that the market is rational.
Option B:that all investors make rational decisions.
Option C:that some investors make irrational decisions.

Answer: A