The Radius of Convergence of the Power Series $\sum _ { n = 1 } ^ { \infty } x ^ { n } / n !$

Multiple Choice

The radius of convergence of the power series $\sum _ { n = 1 } ^ { \infty } x ^ { n } / n !$ is

A) 0
B) 1
C) 2
D) $\infty$
E) none of the above