Since the 1930s aircraft manufacturers have tried to build airplanes with frictionless wings, shaped so smoothly and perfectly that the air passing over them would not become turbulent.
wings, shaped so smoothly and perfectly
wings, wings so smooth and so perfectly shaped
wings that are shaped so smooth and perfect
wings, shaped in such a smooth and perfect manner
wings, wings having been shaped smoothly and perfectly so
A选项:it is unclear what is shaped so smoothly and perfectly; it could be either the airplanes or the wings
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