According to the PMBOK Guide, the project manager is responsible for managing the project resources, including materials, and ensuring that they are available and delivered on time. The project manager should also monitor and control the project risks, and implement appropriate responses when they occur. If one important material is still not on site and the delivery date is approaching, the project manager should engage the project team to look for alternatives to find a solution. This means that the project manager should involve the team members who have the relevant expertise, knowledge, and skills to identify and evaluate possible options to overcome the problem, such as using a substitute material, changing the design or scope, or negotiating with the supplier or the client. Engaging the project team to look for alternatives to find a solution will help the project manager to leverage the collective intelligence and creativity of the team, and to find the best solution that meets the project objectives and satisfies the stakeholders. Recording it in the risk register is not a sufficient action, as it does not address the problem or prevent the delay. The project manager should have identified and recorded this risk earlier, and developed a contingency plan to deal with it. Asking the client to help solve the problem is not a good option, as it may damage the relationship and trust between the project manager and the client, and imply that the project manager is not capable of managing the project. The project manager should communicate the problem to the client, but not rely on the client to solve it. Starting procuring this material from another supplier is a risky and costly option, as it may not guarantee the quality, availability, or delivery of the material, and it may incur additional expenses and contractual issues. The project manager should consider this option only after exhausting other alternatives, and with the approval of the relevant stakeholders. References: PMBOK Guide, 6th edition, pages 355-356, 441-442, 456-457.