• New line items inherit the new default targeting and existing line items inherit edits to default geotargeting
• New and existing line items inherit the new insertion order targeting
• Existing and new line items apply the original default targeting
• Existing line items are uneffected and new line items inherit the new default targeting

The correct answer is: Existing line items are uneffected and new line items inherit the new default targeting

Explanation: Default targeting only affects new line items and can’t be used to change the targeting of any existing line items. The targeting set for an advertiser cannot be edited in campaigns, insertion orders, or line items. You must return to the advertiser to edit these targeting settings. This targeting will not affect default line items for programmatic guaranteed deals.

Read more here: https://support.google.com/displayvideo/answer/2948712