The Most Crucial Limitation(s)associated with Causal Methods of Sales Forecasting

The most crucial limitation(s) associated with causal methods of sales forecasting is(are) :

A) the problem of determining future values of the independent or causal variables.
B) the problem of securing unbiased sales estimates from the sales force.
C) that seasonal variations in performance are difficult to precisely estimate.
D) both (b) and (c) .
E) All of the above are crucial limitations of causal methods of sales forecasting.