$($a$)$ The criterion used when selecting the most appropriate RFx method is based on the organization's desired sourcing business model or sourcing continuum. This involves aligning various competitive bidding factors to each of the sourcing business models, considering factors such as the nature of goods$/$services$,$ stakeholder involvement, supplier involvement, frequency of bid, and the time needed to complete the process.

$($b$)$ In the 'Shifting the continuum in practice' section, the article illustrates the practical application of shifting the sourcing continuum using the example of Telia, a telecommunications company. Telia, faced with numerous contracts rooted in transaction$-$based models, conducted a pre$-$study and business model mapping to determine the most appropriate sourcing business model. The complexity and dependency of Telia$$s operations led to the decision to shift to a highly strategic Vested business model. To find the right partner, Telia piloted the University of Tennessee$$s Request for Partner process, down$-$selected three potential partners, and engaged in collaborative workshops. The result was a Vested partnership with Veolia, focused on creating common value and success through innovative and sustainable solutions. The collaboration workshops played a crucial role in defining desired outcomes, guiding principles, and potential innovations for the partnership. The parties formalized their agreement in April $2017$ under the virtual company name of OneTech. write this as a collge student