4・16 A student attempts to find the average of three numbers $x, y$, and $z$ by first finding the average of $x$ and $y$, and then finding the average of that result and $z$. When $x<y<z$, the student's final result is
(A) correct.
(B) always less than $A$.
(C) always greater than $A$.
(D) sometimes less than $A$ and sometimes equal to $A$.
(E) sometimes greater than $A$ and sometimes equal to $A$.
(37th American High School Mathematics Examination, 1986)