$6 \cdot 4(-1)^{(-1)^{(-1)}}$ equals
(A) 1 .
(B) -1 .
(C) $\pm 1$.
(D) undefined.
(1st "Five Sheep Cup" Junior High School Mathematics Competition, 1989)
[Solution] $\because \quad(-1)^{(-1)}=\frac{1}{-1}=-1$,
$$
\therefore \quad(-1)^{(-1)^{(-1)}}=(-1)^{(-1)}=-1 \text {. }
$$

Therefore, the correct choice is $(B)$.