If $\mathrm{f}: \mathbb{R} \rightarrow \mathrm{A}$, defined by $\mathrm{f}(\mathrm{x})=\cos \mathrm{x}+\sqrt{3} \sin \mathrm{x}-1$, is an onto function then $\mathrm{A}=$

• A

  $[-1,2]$
• B

  $[-\sqrt{3}, \sqrt{3}]$
• Correct answer
  C

  $[-3,1]$
• D

  $[-2,2]$

Hence, the correct answer is option: 'C'.