Discounting future cash flows means $\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.$

a$.$reducing future cash flows by the opportunity cost of interest

b$.$multiplying future cash flows by a discount factor

c$.$making future cash flows comparable and capable of being added together

d$.($a$)$ & $($b$),$ but not $($c$)$

e$.($a$),($b$)$ & $($c$)$