To connect the line with missing data points in between, you can use the "Connect data points with line" option in Excel. Here's how:

1. Select the data points you want to connect with a line.
2. Right-click on the selected data points and choose "Format Data Series" from the menu.
3. In the "Format Data Series" pane that appears on the right side of the screen, click on the "Series Options" tab.
4. Under "Plot Series On", choose "Primary Axis" if it's not already selected.
5. Check the box next to "Connect data points with line".
6. Click "Close" to apply the changes.

This should connect the data points with a line, even if there are missing data points in between. The line will simply skip over the missing data points.