Final answer:
Dollar inventory control is the most suitable unit of control for firms with large amounts of inventory at a relatively low per-unit value.
Step-by-step explanation:
The unit of control suitable for firms with large amounts of inventory at a relatively low per-unit value is Dollar inventory control. Dollar inventory control focuses on managing the value of inventory rather than the quantity. It aims to ensure that the dollar value of inventory remains within acceptable levels while minimizing holding costs and maintaining adequate stock.