请教各位大神，为什么The neoclassicial economics model (aka perfect competition model) does not give us any reasons to believe that a more competitive market is more efficient？

Use the adjusted beta estimate for the three stocks to estimate expected return and volatility of the three stocks based on single index (market) model. 怎样用beta 求expected return and volatility... 求帮忙...急... 谁能帮忙答一下给 20论坛币！谢谢！