Which of the following challenges does mean-variance optimisation framework face? A. The inputs are estimated with substantial errors. B. Estimating volatilities and covariances is imprecise and needs long history of data. C. Costly to obtain more observations through higher frequency data e.g. intraday prices to improve estimation precision for means, volatilities, and covariances. D. The computational cost is high due to a large number of inputs. E. All of the above