If we assume a Cobb$-$Douglas production function, where the share of capital is $0\mathrm{.}25$ and the share of labor is $0\mathrm{.}75,$ then the marginal product of labor is equal to

A$)$ Y$/$N

B$)3$Y$/4$N

C$)(3/4)$N

D$)3$K$/4$N

E$)3$N$/4$Y