\textbf{188.} Two moving objects A and B move in a straight path and in the same direction. Their collision is perfectly elastic. The kinetic energy of A equals 4 times the kinetic energy of B. If the mass of A is $2\,\text{kg}$, what is the mass of object B in kilograms?
\begin{itemize}
\item[(1)] $8$
\item[(2)] $4$
\item[(3)] $1$
\item[(4)] $0.5$
\end{itemize}