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You can enable the Multi-select Drop-down List feature, and select multiple items from the drop-down lists in data validation (drop-down list) ranges easily.

1. Click Kutools > Drop-down List > Multi-select Drop-down List > Settings.

2. In the Multi-select Drop-down List Settings dialog, please configure as follows:
(1) Specify the applying scope in the Apply to section. In my case, I specify Current worksheet as applying scope.

• If you need to apply the feature in a certain range, please tick the Specified Range option, and specify the range address into below box;
• If you need to apply the feature to current worksheet, current workbook, or all workbooks, please choose corresponding option from the Specified Scope drop-down list.

(2) Specify the text direction as you need. In my case, I choose Horizontally.
(3) In the Separator box, please enter a delimiter as you need.
(4) It’s optional to tick the Do not add duplicates option only or tick both the Do not add duplicates and Remove Duplicates options as you need.

Tips:
(1) If you don’t want to make duplicates in drop-down cells, please check the Do not add duplicates box only in the Options section;
(2) If you want to remove items which you have specified from the drop-down list, please check both the Do not add duplicates box and the Remove Duplicates box.

3. Click the Ok button to save the settings.

4. Click Kutools > Drop-down List > Multi-select Drop-down List > Enable Multi-select Drop-down List to enable this feature.

Now in the specified applying scope, you can select multiple items from drop-down lists in every cell that you have set data validation (drop-down list) for.

1. This Multi-select Drop-down List feature will turn off after closing the workbook. You need to enable it again by clicking Kutools > Drop-down List > Multi-select Drop-down List when reopening workbook.

2. You can apply the Clear Data Validation Restrictions feature of Kutools for Excel to clear the data validation of drop-down lists from selections.