单选题图所示刚架，EI=常数，结点A的转角是（　　）。（提示：利用转动刚度的概念）<br/> <br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/8325618_0.jpg"><br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/8325618_0_1.png">