`f(x)=sqrt(x+2sqrt(2x-4))+sqrt(x-2sqrt(2x-4))` then
(a) `f(x)` is continuous at all points in its domain
(b) `f(x)` is differentiable at aal points in its domain
(c) `f'(x)=0` for all `x in [2,4)`
(d) Range of function is `[2sqrt2,oo)`