Task: Question Answering
Input (English): Let the function \(f\) be defined by \(f(2k) = 2f(k)\) and \(f(5) = 10\). Which of the following functions could be the definition of \(f(x)\)?
(A)\(f(x) = x + 5\) (B)\(f(x) = x - 5\) (C)\(f(x) = 15 - x \) (D)\(f(x) = 2x\) (E)\(f(x) = x\)
Output (English): D