The number of different values of $a$ for which the equation $x ^ { 3 } - x + a = 0$ has two identical real roots is (A) 0 . (B) 1 . (C) 2 . (D) 3 .
The number of different values of $a$ for which the equation $x ^ { 3 } - x + a = 0$ has two identical real roots is\\
(A) 0 .\\
(B) 1 .\\
(C) 2 .\\
(D) 3 .