图示结构各杆长度均为l,抗弯刚度为EI,AB杆B端弯矩MBA的大小及受拉侧为( )。
A <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23413172_0_1.png">,右侧 B
<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23413172_0_2.png">,左侧 C
<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23413172_0_3.png">,右侧 D
<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23413172_0_4.png">,左侧