To accurately develop a project budget, the project manager must base cost estimates on detailed scope elements. The work breakdown structure (WBS) provides a hierarchical decomposition of all deliverables and work packages. By referencing the WBS along with the project schedule, the project manager can estimate the costs of each component and aggregate them into a total project budget. This approach is known as bottom-up estimating.
Option B relies too much on the high-level charter and sponsor input, which is insufficient for detailed cost planning.
Option C uses analogous estimating, which is less precise and appropriate only when limited information is available.
Option D is an informal and unreliable estimation method.
References:
PMBOK Guide - Seventh Edition, Planning Performance Domain
PMBOK Guide - Sixth Edition, Sections 7.2 (Estimate Costs) and 7.3 (Determine Budget)
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