单选题图示结构A点的弯矩为以下何值？（　　）<br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251122/18930545_0.jpg"><br/> A.Pl<br/> B.<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251122/18930545_0_1.jpg"><br/> C.0<br/> D.2Pl