Yes, it is possible to connect the tops of columns in a multi-column chart with a line to show a trendline for the series. Here are the steps to follow:

1. Select the chart you want to modify.
2. Click on the "Design" tab in the ribbon.
3. Click on the "Select Data" button in the "Data" group.
4. In the "Select Data Source" dialog box, click on the "Edit" button under [b]"Legend Entries (Series)."
5. In the "Edit Series" dialog box, select the series you want to modify and click on the "Edit" button under "Series Values."
6. In the "Edit Series" dialog box, select the range of cells that contain the data for the series.
7. Click on the "OK" button to close the "Edit Series" dialog box.
8. Click on the "OK" button to close the "Select Data Source" dialog box.
9. Right-click on one of the columns in the series you just modified and select "Format Data Series" from the context menu.
10. In the "Format Data Series" pane, select the "Fill & Line" tab.
11. Under "Line," select the "Solid line" option.
12. Under "Dash Type," select the type of line you want to use to connect the tops of the columns.
13. Under "Cap Type," select the "Flat" option.
14. Adjust the "Width" and "Color" options as desired.
15. Click on the "Close" button to close the "Format Data Series" pane.

The line should now connect the tops of the columns in the series you modified. You can repeat these steps for any other series in the chart that you want to modify.