Answer:
c.They must be an integral part of the finished product and a significant portion of the total product cost.
Explanation:
Direct material is the key component of finished product, it is what is called finished product after processing.
It might be combination of so many raw materials or that it might be alone.
Thus, it forms an integral part of finished product and also it involves a huge share that is clearly identifiable in the total cost as raw material.
Which is because generally overheads do not have that share in cost, as much as that of raw materials.