Auditors have to maintain objectivity and be aware of anything that might affect their judgement - personal bias, outside pressure, etc. "The system owner stated that the last internal auditor was terminated because the auditor discovered too many deficient controls. " which would be considered outside pressure.
Answer is D. Be aware of any influences that may be exerted on professional judgement.
Independence may be impaired, for example,
by external pressure or influence on auditors; prejudices held by auditors about individuals, audited entities, projects or programmes; recent previous employment with the audited entity; or personal or financial dealings which might cause conflicts of loyalties or of interests. Auditors have an obligation to refrain from becoming involved in
all matters in which they have a vested interest. pg 5 #20
https://www.oas.org/juridico/PDFs/mesicic4_blz_code_%20ag.pdf