\textbf{60.} What is the enrichment process for a sample of uranium?
\begin{itemize}
\item[(1)] Converting as much uranium-235 to uranium-238 as possible
\item[(2)] Converting as much uranium-238 to uranium-235 as possible
\item[(3)] Increasing the percentage of uranium-238 isotopes
\item[(4)] Increasing the percentage of uranium-235 isotopes
\end{itemize}