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 capital market theory, which of the following assumptions allows for the existence of the market portfolio? All investors:
Option A:are price takers.
Option B:have homogeneous expectations.
Option C:plan for the same, single holding period.

Answer: B