Cho $\mathop {\lim }\limits_{x \to 2} f\left( x \right) = 5$. Khi đó, $\mathop {\lim }\limits_{x \to 2} 2f\left( x \right)$ bằng:

A. 5.

B. 2.

C. 10.

D. 7.

Đáp án đúng là: C

Ta có $\mathop {\lim }\limits_{x \to 2} 2f\left( x \right) = \mathop {\lim }\limits_{x \to 2} 2.\mathop {\lim }\limits_{x \to 2} f\left( x \right) = 2.5 = 10$.