\textbf{56 --} The position--time equation of simple harmonic motion in SI is $x = A\cos 5\pi t$. If the average speed over the time interval $t_1 = 0\,\text{s}$ to $t_2 = 0.2\,\text{s}$ is $1.5\,\dfrac{\text{m}}{\text{s}}$, the amplitude of oscillation is how many centimeters?
\begin{itemize}
\item[(1)] $1.5$
\item[(2)] $3$
\item[(3)] $4.5$
\item[(4)] $6$
\end{itemize}
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