单选题图所示的刚架，EI＝常数，各杆长为l，A截面的转角为（　　）。<br/> <br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/8325540_0.png"><br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/8325540_0_1.png">