Assertion (A):  $f\left(x\right)=\frac{\sin \left\{\left[x\right]\pi \right\}}{1+x^2}$ is continuous on R ( where [x] denotes greatest integer function of x).
Reason (R) : Every constant function is continuous on R.

Both A and R are true and R is the correct explanation for A

Both A and R are true and R is not the correct explanation for A 

A is true but R is false

R is true but A is false