Consider the estimated relationship: Y = 50 + 50X + 21Z Based on this regression equation, select all the statements which are True:
A.) Controlling for X, the value of Y decreases by 21 units for unit increase in Z
B.) The average value of Y when X=0 and Z=0 is 50.
C.) Controlling for Z, the value of Y increases by 50 units for 1 unit in X
D.) Controlling for X, the value of Y increases by 100 units for 1 unit increase in Z