Answer:
A. magnitude
Explanation:
As on the correct level it is very difficult to estimate the correct effect of all the changes in portfolio returns, this is because the magnitude is not properly identified.
Thus, here in the give case also the problem is of magnitude that the results can not be predicted properly and there is slight fluctuation.
This is a problem that is common with each portfolio, as the market is changing with unavoidable consequences, accordingly the results are also changing unavoidably.