According to the PMBOK Guide, the project manager should use a participatory approach to develop the project schedule, involving the team members who will perform the work1. This will increase the accuracy and reliability of the schedule estimates, as well as the commitment and ownership of the team2. Therefore, the best option is to organize a planning session with the development team and use their estimations to complete the schedule. Option B is incorrect because changing the delivery date for the project schedule based on the availability of a new contractor may not be feasible or acceptable to the stakeholders. Option C is incorrect because asking the sponsor to provide the desired completion date for project activities may not reflect the realistic effort and duration required to complete the work. Option D is incorrect because using expert judgment to estimate all of the tasks may not account for the variability and uncertainty of the work, and may not involve the input and feedback of the team members. References: 1: PMBOK Guide, 6th edition, section 6.1.2.5, p. 191 2: PMBOK Guide, 6th edition, section 6.5.2.4, p. 218