Final answer:
Generally, editing the default targeting for insertion orders causes all line items to inherit the new targeting unless custom targeting has been set for individual line items, which would then override the default settings.
Correct option is A
Step-by-step explanation:
When a user edits the default targeting for insertion orders, it affects the line items differently depending on the platform being used and how it is configured. Generally, option (a) All line items inherit the new targeting is what one might expect in many advertising systems. This means that upon editing the default targeting, all the associated line items would automatically update to reflect the changes. However, this might not always hold true if the system allows for option (d) where Custom targeting overrides default targeting.
This would mean that any line items with custom-targeting settings would not be affected by changes in the default targeting. It's important to check the specific behavior of the ad management system you are using to know how changes to insertion order defaults will affect line items.