Let P_X = X $X ^ { \prime }$ X)^-1

Multiple Choice

Let P_X = X( $X ^ { \prime }$ X) ^-1 $X ^ { \prime }$ and M_X = I_n - P_X. Then M_X M_X =

A) X( $X ^ { \prime }$ X) ^-1 $X ^ { \prime }$ - P_X.
B) $M _ { X } ^ { 2 }$
C) I_n.
D) M_X.