함수 $\displaystyle F \left (s \right) = \frac{1} {\left (s^2 +1 \right) \left (s^2 +4 \right)}$ 의 역라플라스변환(inverse Laplace transform)은?

• ①$\displaystyle \frac{1} {3} \left (\sin t- \frac{1} {2} \cos 2t \right)$
• ②$\displaystyle \frac{1} {3} \left (\cos t- \frac{1} {2} \sin 2t \right)$
• ③$\displaystyle \frac{1} {3} \left (\sin t- \frac{1} {2} \sin 2t \right)$
• ④$\displaystyle \frac{1} {3} \left (\cos t- \frac{1} {2} \cos 2t \right)$