New PMP Question & Answers with explanation

A buyer and seller are looking at getting into a long-term relationship spanning 10 years. Both parties would like to be protected from the unstable financial conditions of their country, which are beyond their control. What type of contract is appropriate for such a relationship?
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A seller entered into a contract with a buyer. At the end of the project, the seller was reimbursed for the cost of the project but received a low fee based on certain subjective criteria that were specified in the contract. What type of contract is this likely to be?
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A seller began a project that was contracted on a time-and-materials (T&M) basis. Based on the agreed-upon rates and effort, the initial contract amount was $100,000 over a one-year period. However, when the project was completed, the total contract value turned out to be $350,000 over a two-year period. What mechanism could the buyer have used to prevent this unlimited cost growth and schedule change?
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In a multi-phase project, the procurement team decided to close the procurements applicable to a particular phase of the project. What happens to unresolved claims?
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During the procurement process, a contractual relationship is established between a buyer and a seller. During the contract lifecycle, what is the correct sequence in which the following terminology is applied to a seller: Vendor, selected source, and bidder?
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