Based on this excerpt, what behavior does Jack most clearly disapprove of?

Answer:
I believe the answer is a Being deceptive
Explanation:
He stated that he had no brother. He also stated " Under the false pretence of being my brother" and he also uses the words 'Disgraceful Deception'
The behavior that Jack most clearly disapprove of is:
Let's understand what "Importance of Being Earnest" is all about.
"The Importance of Being Earnest" is known to be a play that was written by Oscar Wilde. The play is a comedy that showcases protagonists that maintain fictitious personae in order to run away from their expected social obligations.
We see from the excerpt that the use "disgraceful deception" reveals that Jack disapproves being deceptive.
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