The Largest Set on Which $f ( x ) = \sqrt { x ^ { 2 } + 1 }$

Multiple Choice

The largest set on which $f ( x ) = \sqrt { x ^ { 2 } + 1 }$ is continuous is

A) $( - \infty , \infty )$
B) $( - \infty , 1 ) \cup ( 1 , \infty )$
C) $( - \infty , - 1 ) \cup ( - 1 , \infty )$
D) $( - \infty , - 1 ) \cup ( 1 , \infty )$
E) $( - \infty , - 1 ) \cup ( - 1,1 ) \cup ( 1 , \infty )$