Let #f(x) = (|__x__|)/(x^2 + 1) # where #|__x__|# denotes the greatest integer less than or equal to x. Then?

A. #f# is continuous for all #x#.
B. #f# is continuous only when #x# is an integer.
C. #f# is continuous only when #x# is not an integer.
D. #f# is not continuous at any value of #x#.

I know that the function is continuous at every point except at #x^2 +1 = 0#
But #x^2 = -1# is not a real number.
Please help.