单项选择题
(A)四跨 (B)五跨 (C)七跨 (D)九跨
(A)500mm (B)800mm (C)1000mm (D)1200mm
(A)20mm (B)土20mm (C)±30mm (D)±50mm
(A)±10mm (B)±30mm (C)±43mm (D)±50mm
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