John is a senior auditor at WKW LLP$.$ In $2021,$ he audited Winston Inc., a private medium$-$sized manufacturing firm incorporated in California. He is also the solo shareholder of an investment firm in Cayman Island $($a tax haven$)$ which holds $2,000$ shares of Winston since $2019.$ John violated which of $11$ AICPA audit principles?

A$)$ Appropriate competence principle.

B$)$ Principle on audit fee.

C$)$ Ethical requirements and independence principle.

D$)$ Professional skepticism principle.