承受均布载荷的简支梁如图（a）所示，现将两端的支座同时向梁中间移动l/8，如图（b）所示。两根梁的中点（l/2处）弯矩之比Ma/Mb为（　　）。<br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23818280_0.png"><br/> 图（a）<br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23818280_0_1.png"><br/> 图（b）