How can you ensure that a drop-down list in cells D2:D20 does not allow blanks?

The correct choice revolves around preventing users from leaving a selected drop-down list cell blank. Unchecking the Ignore Blank check box ensures that no blanks are allowed in the specified range, which in this case is D2:D20. This setting enforces a rule for the data validation for that range, meaning a user must select a valid entry from the drop-down list and cannot leave the cell empty.

When the Ignore Blanks option is selected, users are permitted to leave a cell blank after making a selection from the drop-down list, thereby allowing for invalid inputs. Therefore, unchecking this box is crucial for maintaining data integrity and compliance with the expected inputs from the drop-down options.

The other options provided do not directly address the requirement of disallowing blank entries in the list. Selecting the Allow List option pertains to enabling data validation via a list, but it does not inherently preclude blanks. Limiting the list items to a specific range merely defines where the list data is sourced from, which can still allow for blank selections unless the corresponding validation setting is adjusted.