Let f (x) be a function such that ${\mathrm{f}}^{\mathrm{\prime }}\left(\mathrm{x}\right)={\log }_{1/3}\left[{\log }_3(\sin \mathrm{x}+\mathrm{a})\right]$.If f(x) is decreasing for all real values of x, then

• A

  $\mathrm{a}\in (1,4)$

• B

  $\mathrm{a}\in [4,\mathrm{\infty })$

• C

  $\mathrm{a}\in (2,3)$

• D

  $\mathrm{a}\in [2,\mathrm{\infty })$