In the Previous Problem, If $F ( \alpha ) = e ^ { - \alpha } \text {, then } f ( x )$

Multiple Choice

In the previous problem, if $F ( \alpha ) = e ^ { - \alpha } \text {, then } f ( x )$ is

A) $x$
B) $1$
C) $1 / \left( \pi \left( 1 + x ^ { 2 } \right) \right)$
D) $2 / \left( \pi \left( 1 + x ^ { 2 } \right) \right)$
E) 0