Which of the Following Best Explains 'Optimal Batch Size

Which of the following best explains 'optimal batch size'? 

A)  The optimal batch size is achieved when the sum of the inventory costs and set up costs per unit produced is lowest. 
B)  The optimal batch size is achieved when the sum of price and the inventory costs is highest. 
C)  The optimal batch size is achieved when the set up costs per unit produced is lowest. 
D)  The optimal batch size is achieved when the inventory costs per unit produced is lowest.