What is the correct past perfect third-person conjugation for irregular verb shrink?

The correct past perfect third-person conjugation for the irregular verb "shrink" is had shrunk.

Here's the breakdown:

* Past perfect tense: Used to describe an action that was completed before another past action.

* Third-person singular: Refers to "he," "she," or "it."

* Irregular verb: "Shrink" has an irregular past participle form ("shrunk").

Therefore, the full form is "had shrunk."