Which of the following functions lie in the span of the vector-valued functions
$$
\mathbf{f}_1(x)=\left(\begin{array}{l}
1 \\
x
\end{array}\right), \quad \mathbf{f}_2(x)=\left(\begin{array}{c}
x \\
1
\end{array}\right), \quad \mathbf{f}_3(x)=\left(\begin{array}{c}
x \\
2 x
\end{array}\right) ?
$$
(a) $\left(\begin{array}{l}2 \\ 1\end{array}\right)$,
(b) $\left(\begin{array}{c}1-2 x \\ 1-x\end{array}\right)$,
(c) $\left(\begin{array}{c}1-2 x \\ -1-x\end{array}\right)$,
(d) $\left(\begin{array}{c}1+x^2 \\ 1-x^2\end{array}\right)$,
(e) $\left(\begin{array}{c}2-x \\ 0\end{array}\right)$