let us assume that x>0
so
f(x)=3x and g(x)=x/3
f(g(x))=x=h(x)
sin-1(x.x.x.x.x.....x)(n times)
we get
sin-1xn
and we know that the domain of sin-1x is [0 ,1](x>0)
if x<0
we will get f(g(x))=x
so again
sin-1xn
and we know that the domain of sin-1x is [-1 ,0](x<0)
so A is correct