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Some drop-down comboboxes could be switched directly. You could just click the combobox and choose "Loop switch combobox". And then you could loop click the values in the drop-down menu.
Some drop-down comboboxes couldn’t be switched directly. In this case, you need to manually add a “Loop” action and enter the XPath of the drop-down list. See the step 2 in Scrape Web Data from A Drop-Down Menu 1.