C (Significant effort and time): In a Waterfall model, changes introduced after the design phase require rework of multiple design documents, validations, and downstream impacts on implementation and testing. This leads to significant delays and resource consumption compared to more flexible models like Agile.

Other options explained:

A: Creativity is not the primary impact.

B: Rework is true but doesn’t fully capture the scope of additional effort.

D: Waterfall does not provide inherent flexibility to absorb late changes.

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