A start-up biomedical engineering firm has begun manufacturing a drug-coated bimetallic stent, which is a thin wire mesh tube inserted in clogged coronary arteries to prop them open and prevent future heart attacks. Identify the following costs of manufacturing the stents as either sunk or avoidable costs now that the firm has received final approval from the food and drug administration (FDA) and manufacturing is currently in progress:

a. Biomedical research and development costs to design the heart stent.

b. Costs of running clinical trials to win FDA approval to begin making and selling the stent to cardiologists.

c. Labor costs to operate the manufacturing equipment.

d. Cost of drug, high-grade stainless steel, and titanium used in making the stents.

e. Set-up cost incurred to install the manufacturing equipment and train workers to operate the equipment.

f. Legal costs of filing a patent application.

Please explain each of the choices.