$\displaystyle \lim _ {x \rightarrow 0^+} {f \left (x \right)} =3, \lim _ {x \rightarrow 0^-} {f \left (x \right)} =1$ 일 때, $\displaystyle \lim _ {x \rightarrow 0 ^ {-}} {\left. \left \{f \left (x ^ {3} +x ^ {2} \right) -f \left (-x ^ {3} \right) \right. \right \}}$ 의 값은?

• ①$-2$
• ②$0$
• ③$2$
• ④$6$