A Valid Multiple Linear Regression (MLR) Is Characterized by All

A valid Multiple Linear Regression (MLR) is characterized by all of these except _______________________.  

A) It is an assumption that the X's (inputs) are not correlated to each other
B) The X's (inputs) are assumed to be independent of each other
C) MLR is conducted based on a deliberate form of experimentation
D) The Residuals from MLR analysis have to be Normally Distributed