The function \(f(x) = \begin{cases} \frac{x^2-1}{x^3+1} & \quad \text{} x≠1 \text{ }\\ P & \quad \text{} x=-1 \text{ } \end{cases}\) is not defined for x = -1. The value of f(-1) so that the function extended by this value is continuous is ...
(a) 2/3
(b) -2/3
(c) 1
(d) 0