What Is the Unit of K in the Following Rate $\frac { \mathrm { M } ^ { 2 } } { \mathrm {~s} }$

What is the unit of k in the following rate law?
Rate = k[X][Y]

A) mol L^-1 s^-1
B) mol L^-1 s
C) L mol^-1 s^-1
D) $\frac { \mathrm { M } ^ { 2 } } { \mathrm {~s} }$
E) $\frac { \mathrm { s } } { \mathrm { M } ^ { 2 } }$