Without using formulas, provide a definition of payback period. Select one: O a. None of the suggested answers O b. A project analysis tool that measures the acceptability of a project through the difference between a project's initial investment and whether the present value of its cash flow will repay the investment O c. A project analysis tool that measures the acceptability of a project by determining the amount of profit that can be expected based on an investment made. O d. A project analysis tool that measures the acceptability of a project by determining the length of time required for an investment's discounted cash flows to equal its initial cost. e. A ranking method used to assess projects. Pl greater than 1 signify positive NPV projects, while Pl less than 1 signify negative NPV projects