The Following Are All Least Squares Assumptions with the Exception $u _ { i }$

The following are all least squares assumptions with the exception of: a. The conditional distribution of $u _ { i }$ given $X _ { i }$ has a mean of zero.
b. The explanatory variable in regression model is normally distributed.
c. $\left( X _ { i } , Y _ { i } \right) , i = 1 , \ldots , n$ are independently and identically distributed.
d. Large outliers are unlikely.