正确答案是B,但是为何C不对呢？想来想去还是不懂！谢谢各位指教！！！
651.Since the 1930’s 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.
(A) wings, shaped so smoothly and perfectly
(B) wings, wings so smooth and so perfectly shaped
(C) wings that are shaped so smooth and perfect
(D) wings, shaped in such a smooth and perfect manner
(E) wings, wings having been shaped smoothly and perfectly so | 
