If f(x) is an even function and a is a positive real number, then $$\int_{ – {\text{a}}}^{\text{a}} {{\text{f}}\left( {\text{x}} \right){\text{dx}}} $$ equals A. 0 B. a C. 2a D. $$2\int_0^{\text{a}} {{\text{f}}\left( {\text{x}} \right){\text{dx}}} $$

The correct answer is $\boxed{\text{D}}$.

An even function is a function $f$ such that $f(-x) = f(x)$ for all $x$.

The integral $\int_{-a}^a f(x) dx$ is the area under the curve $y=f(x)$ between $x=-a$ and $x=a$.

If $f$ is even, then the graph of $y=f(x)$ is symmetric about the $y$-axis. This means that the area under the curve between $x=-a$ and $x=a$ is the same as the area under the curve between $x=0$ and $x=a$.

Therefore, $\int_{-a}^a f(x) dx = 2 \int_0^a f(x) dx$.