The correct answers are 'it is easy to drive down costs' (as you can pit the suppliers against each other) and
'low risk of failure to supply' (if one supplier can't provide what you need, the other supplier might be able to).
Economies of scale and supplier loyalty are advantages of single-sourcing.
There is a risk of failure to supply is a risk associated with single sourcing.
There's a useful table of advantages and disadvantages of single / multi sourcing on p.22. Types of sourcing is a key topic for the exam.

Prohibiting trade union membership is a violation of workers' rights and international labor standards. Such a practice indicates potential non-compliance with ethical sourcing principles and necessitates further investigation. Ensuring that suppliers respect workers' rights to association is fundamental to ethical procurement.
Reference:
CIPS Level 4 Diploma in Procurement and Supply, L4M4 Study Guide, Section 3.3.1:Application of the CIPS Code of Conduct

Governance of ethical and sustainable behaviour focuses on ensuring suppliers have the right systems, policies, and transparency measures in place. Reviewing insurance clauses ensures suppliers are prepared to manage liability and risks responsibly. Checking conflict of interest registers promotes transparency and prevents corruption. By contrast, NDAs protect confidentiality but are not primarily ethical governance tools, and simply checking "up-to-date policies" without context may not guarantee compliance. CIPS highlights governance mechanisms such as audits, policy reviews, and conflict registers as integral to monitoring ethical performance and ensuring accountability.
Reference: CIPS L4M4 Study Guide (v2), LO: "Implementation" - governance measures, monitoring supplier ethics.

Informing suppliers of non-conformances and improvement opportunities supports responsible sourcing by promoting continuous improvement. Preparing a report for supplier review also aligns with transparency and collaborative improvement, integral to ethical sourcing standards.