An Estimator $\hat { \mu }_Y$ Of the Population Value $\mu_Y$ Is More Efficient When Compared to Another Estimator

Multiple Choice

An estimator $\hat { \mu }_Y$ of the population value $\mu_Y$ is more efficient when compared to another estimator $\bar { \mu }_Y$ , if

A) E( $\hat { \mu }_y$ ) > E( $\bar { \mu }_Y$ ) .
B) it has a smaller variance.
C) its c.d.f. is flatter than that of the other estimator.
D) both estimators are unbiased, and var( $\hat { \mu }_Y$ ) < var( $\bar { \mu }_y$ ) .