Return on Assets is a good way to measure the opportunity costs of an investment. If a company has a Return on Assets of 12% and a line of Credit at 6%, how should they manage their cash flow? What is the correct answer? Explanation needed

a) they should use the line of credit to finance expansion and use the cash to cover project level cash flow.

b) They should use the line of credit for project cash flow, and use the company's cash to expand business

c). they should never use debt to finance operation

d). they should get out of the construction business because the RoA is horrible.