Final answer:
The audit firm must ensure the independence of the other CPA firm when using its services for part of an engagement on a client's subsidiary.
Step-by-step explanation:
When an audit firm uses another CPA firm to perform part of the engagement on a client's subsidiary, it is not required to merge with the other CPA firm or list the other firm in the footnotes to the client's financial statements. Instead, the primary audit firm must ensure the independence of the other CPA firm of the client. The principal auditor has a responsibility to evaluate the independence and performance of the other auditors to ensure that the audit is conducted with the same rigor and professional standards across all portions of the engagement. It is important for the audit firm to ensure that the other CPA firm is unbiased and can provide objective and reliable audit services to the client's subsidiary. This is necessary for maintaining the integrity and credibility of the audit process.