The Class of Linear Conditionally Unbiased Estimators Consists of A All

Short Answer

The class of linear conditionally unbiased estimators consists of a. all estimators of $\beta _ { 1 }$ that are linear functions of $Y _ { 1 } , \ldots , Y _ { n }$ and that are unbiased, conditional on $X _ { 1 } , \ldots , X _ { n }$ .
b. OLS, WLS, and TSLS.
c. those estimators that are asymptotically normally distributed.
d. all estimators of $\beta _ { 1 }$ that are linear functions of $X _ { 1 } , \ldots , X _ { n }$ and that are unbiased, conditional on $X _ { 1 } , \ldots , X _ { n }$ .