Answer:
D. Fixed costs stay constant in total over a wide range of activity levels.
Step-by-step explanation:
1. The average cost per unit is computed by 
= Total cost ÷ number of units 
It does not predict the total cost at different levels 
2. The direct cost includes direct material, direct labor, etc. It only includes variable cost not fixed cost 
Hence, this option is wrong 
3. The manufacturing overhead comprises both types of cost i.e fixed cost and the variable cost 
Hence, this option is wrong 
4. The fixed cost remain the same whether production level changes or not 
Therefore, this option is right