Cho tam thức \(f(x) = {\rm{a}}{{\rm{x}}^2} + bx + c,{\rm{(a}} \ne {\rm{0),}}\,\,\Delta {\rm{ = }}{{\rm{b}}^2} - 4ac\).

A. \(\left\{ \begin{array}{l}
a < 0\\
\Delta  \le 0
\end{array} \right.\)

B. \(\left\{ \begin{array}{l}
a \le 0\\
\Delta  < 0
\end{array} \right.\)

C. \(\left\{ \begin{array}{l}
a < 0\\
\Delta  \ge 0
\end{array} \right.\)

D. \(\left\{ \begin{array}{l}
a > 0\\
\Delta  \le 0
\end{array} \right.\)