Classify each of the following activities as unit level, batch level, product level, or facility level for a manufacturer of tennis balls.

\begin{tabular}{|l|l|} \hline \multicolumn{1}{|c|}{ Activity } & \multicolumn{1}{c|}{ Level } \\ \hline 1. Receiving felt shipments & \\ \hline 2. Cutting felt & \\ \hline 3. Forming rubber cores & \\ \hline 4. Reducing electricity usage \\ \hline 5. Calibrating machines & \\ \hline 6. Planning production & \\ \hline \end{tabular}