Explanation:

- When: This option implies that the action of learning about the gifts led to the feeling of delight. It creates a cause-and-effect relationship. Correct

- Though: This suggests contrast, such as feeling delighted despite something, but there's no contrasting action here.

- While: This suggests simultaneity, indicating two things happening at the same time, but the sentence shows a sequence of events.

- Which: This option would be grammatically incorrect here as it is used to add a clause related to the preceding noun.