What is the best considered base used to forecast sales ?

1- Analysing the last five years sales.

2- Checking the trends for each sales item.

3- Comparing the variables for each sales item with the budgeted year sales for the       same item. 

4- Considering The sales variables which are :

     A- The economic conditions.

     B- Comparing the trend of the items prices of the last five years with the                  budgeted year.

     C- Comparing the company prices with the competitors prices.

     D- The compitability of the stock against the demand for the last five years.

     E- THe timing of the availabilty for the stock.