The GLS Estimator Is Defined as
A) $X ^ { \prime }$

Multiple Choice

The GLS estimator is defined as

A) ( $X ^ { \prime }$ ?^-1X) ^-1 ( $X ^ { \prime }$ ?^-1Y) .
B) ( $X ^ { \prime }$ X) ^-1 $X ^ { \prime }$ Y.
C) $A ^ { \prime }$ Y.
D) ( $X ^ { \prime }$ X) ^-1 $X ^ { \prime }$ U.