Why is a STATIC budget less useful than a FLEXIBLE budget?

A static budget compares the actual cost to the budgeted cost (based on the actual level of Roduction).

A static budget compares the budgeted cost this year to the budgeted cost last year.

I A static budget compares the actual cost this year to the actual cost last year.

A static budget compares the actual cost to the budgeted cost (based on the budgeted level of production).