问题如下：
Which of the following makes the existence of market portfolio in the capital market theory?
选项：
A.All investors are price takers.
B.All investors have homogeneous expectations.
C.All investors have the same, single holding period.
解释：
B is correct.
Homogeneous expectations assumption claims that all investors are rational and would use the same way to analyze securities, meaning that all investors adopt the same probability distributions, the same inputs for future cash flows and would finally reach to the same valuations for the securities. As a consequence, the market portfolio, which is also perceived as the same optimal risky portfolio, is generated.
C为什么不对，讲义上有这句话
