Assume, in analyzing alternative proposals, that Proposal A has a useful life of $5$ years and Proposal B has a useful life of $8$ years. What is one widely used method that makes the proposals comparable?

a$.$ Ignore the useful lives of $5$ and $8$ years and compute the average rate of return.

b$.$ Ignore the fact that Proposal A has a useful life of $5$ years and treat it as if it has a useful life of $8$ years.

c$.$ Adjust the life of Proposal A to a time period that is equal to that of Proposal B by estimating a residual value at the end of Year $5.$

d$.$ Ignore the useful lives of $5$ and $8$ years and find an average $(6(1)/(2)$ years$).$