单选题图所示，已知超静定梁支座反X1=3qL/8，跨中央截面的弯矩值为（　　）。<br/> <br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/8325577_0.jpg"><br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/8325577_0_1.png">