问题
以下关于【函数左导数】的描述中正确的是哪项？选项
[A]. $\lim_{x \rightarrow x_{0}^{\color{Red}{-}}}$ $\frac{f(x) + f(x_{0})}{x + x_{0}}$[B]. $\lim_{x \rightarrow x_{0}^{\color{Red}{-}}}$ $\frac{f(x) – f(x_{0})}{x + x_{0}}$
[C]. $\lim_{x \rightarrow x_{0}^{\color{Red}{+}}}$ $\frac{f(x) – f(x_{0})}{x – x_{0}}$
[D]. $\lim_{x \rightarrow x_{0}^{\color{Red}{-}}}$ $\frac{f(x) – f(x_{0})}{x – x_{0}}$
$f_{\color{Red}{-}}^{‘}(x_{0})$ $=$ $\lim_{x \rightarrow x_{0}^{\color{Red}{-}}}$ $\frac{f(x) – f(x_{0})}{x – x_{0}}$