Khẳng định đúng là

A. \(\mathop {\lim }\limits_{x \to {x_0}} f\left( x \right) = a \Leftrightarrow \mathop {\lim }\limits_{x \to x_0^ + } f\left( x \right) = a\)

B. \(\mathop {\lim }\limits_{x \to {x_0}} f\left( x \right) = a \Leftrightarrow \mathop {\lim }\limits_{x \to x_0^ - } f\left( x \right) = a\)

C. \(\mathop {\lim }\limits_{x \to {x_0}} f\left( x \right) = a \Leftrightarrow \mathop {\lim }\limits_{x \to x_0^ + } f\left( x \right) = \mathop {\lim }\limits_{x \to x_0^ - } f\left( x \right) = a\)

D. \(\mathop {\lim }\limits_{x \to {x_0}} f\left( x \right) = a \Leftrightarrow \mathop {\lim }\limits_{x \to x_0^ + } f\left( x \right) = \mathop {\lim }\limits_{x \to x_0^ - } f\left( x \right)\)