单选题图所示结构取图（b）为力法基本体系，El为常数，下列哪项是错误的[A8] ?（　　）<br/> <br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/8325528_0.jpg"><br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/8325528_0_1.png">