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[主观题]
the following beam with isosceles trapezoid (等腰梯形) cross section is under pure bending m. b = 3b, h = 2b, then
The following beam with isosceles trapezoid (等腰梯形) cross section is under pure bending M. B = 3b, h = 2b, then= ().
A、5/7
B、4/7
C、2/3
D、1/2
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