A company should stop making a part internally and buy externally when:

A.

the unavoidable costs are less than the avoidable costs to make the part externally

B.

the offer to buy the part is greater than the cost to internally make the part

C.

the relevant costs to make the part is less than the cost to buy the part externally

D.

the relevant costs to make the part is greater than the cost to buy the part externally