Which one of the following statements is true? O a. When an explanatory variable is dropped from a multiple regression model, the coefficient of multiple determination can increase. O b. When an additional explanatory variable is introduced into a multiple regression model, the adjusted r2 can never decrease. O c. When an explanatory variable is dropped from a multiple regression model, the adjusted r2 can increase. O d. None of the suggested answers are correct. O e. When an additional explanatory variable is introduced into a multiple regression model, the coefficient of multiple determination will moderately decrease