Comprehensive and Detailed Explanation:
Partnering is most suitable in scenarios involving high-risk contracts, where the complexity, uncertainty, or strategic importance of the procurement necessitates close collaboration between the buyer and supplier. In such cases, a partnership allows for shared risk management, joint problem-solving, and mutual investment in achieving long-term objectives. This approach is less appropriate for low-cost, low-risk, or commoditized items where transactional relationships suffice.
Reference:
CIPS L4M6 Study Guide

This is a threat of a new entrant. The competitor has now entered the washing machine market and is competing directly with you. This is not a threat of substitution as it is the same product. A substitution would be if they invented a new product that washed clothes and people started buying this instead of washing machines. There are many questions in the exam on Porter's 5 Forces - see p. 39

The first step is to obtain business approval to terminate. If Senior Management don't give approval, then the rest of the stages can't happen and Sandra will be stuck with her current banana supplier. There's a good diagram on p.109 detailing the steps to supplier termination.

The correct answer is 'No- good levels of communication can exist in other types of relationships'. The study guide makes a point that not all good buyer: supplier relationships are partnerships. In fact 70% on supplier relationships will not be partnerships (according to Lambert who is quoted on p.131)

An adversarial relationship is highly competitive, often win:lose, focusing on cost and negotiation power rather than collaboration. It contrasts with partnerships or strategic alliances.