Tina was calculating the NPV and IRR for several projects. After performing calculations for one specific project, she realized she had made an error in her calculations. What might have made Tina aware of the error?

a) Her NPV was negative but the IRR was higher than the companys required rate of return.

b) Her NPV was negative but the IRR was lower than the companys required rate of return.

c) Her NPV was zero and her IRR was equal to the companys required rate of return.

d) Her NPV was positive but the IRR was higher than the companys required rate of return.