What is the main difference between a fix and flexible budget?and why-and choose

1. flexible budget can provide less realistic control information than fixed budgets
2. A fixed budget is produced for an entire organisation,but a flexible budget is applicable only to a single department
3. A fixed budget is based on specific level of production/sales and a flexible budget can be prepared for any production level
4. A flexible budget considers only variable costs, but a fixed budget considers all costs